[PATCH 0/9] reftable: optimize write performance

[PATCH 0/9] reftable: optimize write performance

[Patrick Steinhardt]

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Hi,

this is my first patch series taking an actual look at write performance
for the reftable backend. This series addresses two major pain points:

  - Duplicate directory/file conflict checks when writing refs.

  - Allocation churn when compressing log blocks.

Overall though I found that there is not much of a point to investigate
write performance in the reftable library itself, at least not right
now. This is mostly because the write performance is heavily dominated
by random ref reads. And while past patch series have optimized scanning
through refs linearly, seeking random refs isn't well-optimized yet. So
once all in-flight series relating to reftable performance have landed I
will focus on random ref reads next.

For the bigger picture, the following benchmarks show perfomance
compared to the "files" backend after applying this patch series.

Writing many refs in a single transaction:

  Benchmark 1: update-ref: create many refs (refformat = files, refcount = 100000)
    Time (mean ± σ):     10.085 s ±  0.057 s    [User: 1.876 s, System: 8.161 s]
    Range (min … max):   10.013 s … 10.202 s    10 runs

  Benchmark 2: update-ref: create many refs (refformat = reftable, refcount = 100000)
    Time (mean ± σ):      2.768 s ±  0.018 s    [User: 1.381 s, System: 1.383 s]
    Range (min … max):    2.745 s …  2.804 s    10 runs

  Summary
    update-ref: create many refs (refformat = reftable, refcount = 100000) ran
      3.64 ± 0.03 times faster than update-ref: create many refs (refformat = files, refcount = 100000)

And for writing many refs sequentially in separate transactions:

  Benchmark 1: update-ref: create refs sequentially (refformat = files, refcount = 10000)
    Time (mean ± σ):     40.286 s ±  0.086 s    [User: 22.241 s, System: 17.912 s]
    Range (min … max):   40.166 s … 40.410 s    10 runs

  Benchmark 2: update-ref: create refs sequentially (refformat = reftable, refcount = 10000)
    Time (mean ± σ):     44.046 s ±  0.137 s    [User: 23.790 s, System: 20.146 s]
    Range (min … max):   43.813 s … 44.301 s    10 runs

  Summary
    update-ref: create refs sequentially (refformat = files, refcount = 10000) ran
      1.09 ± 0.00 times faster than update-ref: create refs sequentially (refformat = reftable, refcount = 10000)

This is to the best of my knowledge last area where the "files" backend
outperforms the "reftable" backend. This is partially also due to the
fact that writes perform auto-compaction with the "reftable" backend.

Patrick

Patrick Steinhardt (9):
  refs/reftable: fix D/F conflict error message on ref copy
  refs/reftable: perform explicit D/F check when writing symrefs
  refs/reftable: skip duplicate name checks
  refs/reftable: don't recompute committer ident
  reftable/writer: refactorings for `writer_add_record()`
  reftable/writer: refactorings for `writer_flush_nonempty_block()`
  reftable/block: reuse zstream when writing log blocks
  reftable/block: reuse compressed array
  reftable/writer: reset `last_key` instead of releasing it

 refs/reftable-backend.c    |  80 ++++++++++++++++++-------
 reftable/block.c           |  83 ++++++++++++++++----------
 reftable/block.h           |   4 ++
 reftable/writer.c          | 119 ++++++++++++++++++++++++-------------
 t/t0610-reftable-basics.sh |  35 ++++++++++-
 5 files changed, 227 insertions(+), 94 deletions(-)

-- 
2.44.GIT


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[PATCH 1/9] refs/reftable: fix D/F conflict error message on ref copy

[Patrick Steinhardt]

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The `write_copy_table()` function is shared between the reftable
implementations for renaming and copying refs. The only difference
between those two cases is that the rename will also delete the old
reference, whereas copying won't.

This has resulted in a bug though where we don't properly verify refname
availability. When calling `refs_verify_refname_available()`, we always
add the old ref name to the list of refs to be skipped when computing
availability, which indicates that the name would be available even if
it already exists at the current point in time. This is only the right
thing to do for renames though, not for copies.

The consequence of this bug is quite harmless because the reftable
backend has its own checks for D/F conflicts further down in the call
stack, and thus we refuse the update regardless of the bug. But all the
user gets in this case is an uninformative message that copying the ref
has failed, without any further details.

Fix the bug and only add the old name to the skip-list in case we rename
the ref. Consequently, this error case will now be handled by
`refs_verify_refname_available()`, which knows to provide a proper error
message.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 refs/reftable-backend.c    |  3 ++-
 t/t0610-reftable-basics.sh | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index e206d5a073..0358da14db 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -1351,7 +1351,8 @@ static int write_copy_table(struct reftable_writer *writer, void *cb_data)
 	/*
 	 * Verify that the new refname is available.
 	 */
-	string_list_insert(&skip, arg->oldname);
+	if (arg->delete_old)
+		string_list_insert(&skip, arg->oldname);
 	ret = refs_verify_refname_available(&arg->refs->base, arg->newname,
 					    NULL, &skip, &errbuf);
 	if (ret < 0) {
diff --git a/t/t0610-reftable-basics.sh b/t/t0610-reftable-basics.sh
index 686781192e..055231a707 100755
--- a/t/t0610-reftable-basics.sh
+++ b/t/t0610-reftable-basics.sh
@@ -730,6 +730,39 @@ test_expect_success 'reflog: updates via HEAD update HEAD reflog' '
 	)
 '
 
+test_expect_success 'branch: copying branch with D/F conflict' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit A &&
+		git branch branch &&
+		cat >expect <<-EOF &&
+		error: ${SQ}refs/heads/branch${SQ} exists; cannot create ${SQ}refs/heads/branch/moved${SQ}
+		fatal: branch copy failed
+		EOF
+		test_must_fail git branch -c branch branch/moved 2>err &&
+		test_cmp expect err
+	)
+'
+
+test_expect_success 'branch: moving branch with D/F conflict' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit A &&
+		git branch branch &&
+		git branch conflict &&
+		cat >expect <<-EOF &&
+		error: ${SQ}refs/heads/conflict${SQ} exists; cannot create ${SQ}refs/heads/conflict/moved${SQ}
+		fatal: branch rename failed
+		EOF
+		test_must_fail git branch -m branch conflict/moved 2>err &&
+		test_cmp expect err
+	)
+'
+
 test_expect_success 'worktree: adding worktree creates separate stack' '
 	test_when_finished "rm -rf repo worktree" &&
 	git init repo &&
-- 
2.44.GIT


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Re: [PATCH 1/9] refs/reftable: fix D/F conflict error message on ref copy

[Junio C Hamano]

Patrick Steinhardt <ps@pks.im> writes:

> The `write_copy_table()` function is shared between the reftable
> implementations for renaming and copying refs. The only difference
> between those two cases is that the rename will also delete the old
> reference, whereas copying won't.
>
> This has resulted in a bug though where we don't properly verify refname
> availability. When calling `refs_verify_refname_available()`, we always
> add the old ref name to the list of refs to be skipped when computing
> availability, which indicates that the name would be available even if
> it already exists at the current point in time. This is only the right
> thing to do for renames though, not for copies.
>
> The consequence of this bug is quite harmless because the reftable
> backend has its own checks for D/F conflicts further down in the call
> stack, and thus we refuse the update regardless of the bug. But all the
> user gets in this case is an uninformative message that copying the ref
> has failed, without any further details.
>
> Fix the bug and only add the old name to the skip-list in case we rename
> the ref. Consequently, this error case will now be handled by
> `refs_verify_refname_available()`, which knows to provide a proper error
> message.

OK.  Nicely described.  Instead of letting the reftable code
downstream to notice an update that was left uncaught by an extra
element in &skip, we will let refs_verify_refname_available() to
catch it at the right place.  Makes sense.

> Signed-off-by: Patrick Steinhardt <ps@pks.im>
> ---
>  refs/reftable-backend.c    |  3 ++-
>  t/t0610-reftable-basics.sh | 33 +++++++++++++++++++++++++++++++++
>  2 files changed, 35 insertions(+), 1 deletion(-)
>
> diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
> index e206d5a073..0358da14db 100644
> --- a/refs/reftable-backend.c
> +++ b/refs/reftable-backend.c
> @@ -1351,7 +1351,8 @@ static int write_copy_table(struct reftable_writer *writer, void *cb_data)
>  	/*
>  	 * Verify that the new refname is available.
>  	 */
> -	string_list_insert(&skip, arg->oldname);
> +	if (arg->delete_old)
> +		string_list_insert(&skip, arg->oldname);
>  	ret = refs_verify_refname_available(&arg->refs->base, arg->newname,
>  					    NULL, &skip, &errbuf);
>  	if (ret < 0) {
> diff --git a/t/t0610-reftable-basics.sh b/t/t0610-reftable-basics.sh
> index 686781192e..055231a707 100755
> --- a/t/t0610-reftable-basics.sh
> +++ b/t/t0610-reftable-basics.sh
> @@ -730,6 +730,39 @@ test_expect_success 'reflog: updates via HEAD update HEAD reflog' '
>  	)
>  '
>  
> +test_expect_success 'branch: copying branch with D/F conflict' '
> +	test_when_finished "rm -rf repo" &&
> +	git init repo &&
> +	(
> +		cd repo &&
> +		test_commit A &&
> +		git branch branch &&
> +		cat >expect <<-EOF &&
> +		error: ${SQ}refs/heads/branch${SQ} exists; cannot create ${SQ}refs/heads/branch/moved${SQ}
> +		fatal: branch copy failed
> +		EOF
> +		test_must_fail git branch -c branch branch/moved 2>err &&
> +		test_cmp expect err
> +	)
> +'
> +
> +test_expect_success 'branch: moving branch with D/F conflict' '
> +	test_when_finished "rm -rf repo" &&
> +	git init repo &&
> +	(
> +		cd repo &&
> +		test_commit A &&
> +		git branch branch &&
> +		git branch conflict &&
> +		cat >expect <<-EOF &&
> +		error: ${SQ}refs/heads/conflict${SQ} exists; cannot create ${SQ}refs/heads/conflict/moved${SQ}
> +		fatal: branch rename failed
> +		EOF
> +		test_must_fail git branch -m branch conflict/moved 2>err &&
> +		test_cmp expect err
> +	)
> +'
> +
>  test_expect_success 'worktree: adding worktree creates separate stack' '
>  	test_when_finished "rm -rf repo worktree" &&
>  	git init repo &&

[PATCH 2/9] refs/reftable: perform explicit D/F check when writing symrefs

[Patrick Steinhardt]

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We already perform explicit D/F checks in all reftable callbacks which
write refs, except when writing symrefs. For one this leads to an error
message which isn't perfectly actionable because we only tell the user
that there was a D/F conflict, but not which refs conflicted with each
other. But second, once all ref updating callbacks explicitly check for
D/F conflicts, we can disable the D/F checks in the reftable library
itself and thus avoid some duplicated efforts.

Refactor the code that writes symref tables to explicitly call into
`refs_verify_refname_available()` when writing symrefs.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 refs/reftable-backend.c    | 20 +++++++++++++++++---
 t/t0610-reftable-basics.sh |  2 +-
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 0358da14db..8a54b0d8b2 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -1217,6 +1217,7 @@ static int reftable_be_pack_refs(struct ref_store *ref_store,
 struct write_create_symref_arg {
 	struct reftable_ref_store *refs;
 	struct reftable_stack *stack;
+	struct strbuf *err;
 	const char *refname;
 	const char *target;
 	const char *logmsg;
@@ -1239,6 +1240,11 @@ static int write_create_symref_table(struct reftable_writer *writer, void *cb_da
 
 	reftable_writer_set_limits(writer, ts, ts);
 
+	ret = refs_verify_refname_available(&create->refs->base, create->refname,
+					    NULL, NULL, create->err);
+	if (ret < 0)
+		return ret;
+
 	ret = reftable_writer_add_ref(writer, &ref);
 	if (ret)
 		return ret;
@@ -1280,12 +1286,14 @@ static int reftable_be_create_symref(struct ref_store *ref_store,
 	struct reftable_ref_store *refs =
 		reftable_be_downcast(ref_store, REF_STORE_WRITE, "create_symref");
 	struct reftable_stack *stack = stack_for(refs, refname, &refname);
+	struct strbuf err = STRBUF_INIT;
 	struct write_create_symref_arg arg = {
 		.refs = refs,
 		.stack = stack,
 		.refname = refname,
 		.target = target,
 		.logmsg = logmsg,
+		.err = &err,
 	};
 	int ret;
 
@@ -1301,9 +1309,15 @@ static int reftable_be_create_symref(struct ref_store *ref_store,
 
 done:
 	assert(ret != REFTABLE_API_ERROR);
-	if (ret)
-		error("unable to write symref for %s: %s", refname,
-		      reftable_error_str(ret));
+	if (ret) {
+		if (err.len)
+			error("%s", err.buf);
+		else
+			error("unable to write symref for %s: %s", refname,
+			      reftable_error_str(ret));
+	}
+
+	strbuf_release(&err);
 	return ret;
 }
 
diff --git a/t/t0610-reftable-basics.sh b/t/t0610-reftable-basics.sh
index 055231a707..12b0004781 100755
--- a/t/t0610-reftable-basics.sh
+++ b/t/t0610-reftable-basics.sh
@@ -255,7 +255,7 @@ test_expect_success 'ref transaction: creating symbolic ref fails with F/D confl
 	git init repo &&
 	test_commit -C repo A &&
 	cat >expect <<-EOF &&
-	error: unable to write symref for refs/heads: file/directory conflict
+	error: ${SQ}refs/heads/main${SQ} exists; cannot create ${SQ}refs/heads${SQ}
 	EOF
 	test_must_fail git -C repo symbolic-ref refs/heads refs/heads/foo 2>err &&
 	test_cmp expect err
-- 
2.44.GIT


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[PATCH 3/9] refs/reftable: skip duplicate name checks

[Patrick Steinhardt]

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All the callback functions which write refs in the reftable backend
perform D/F conflict checks via `refs_verify_refname_available()`. But
in reality we perform these D/F conflict checks a second time in the
reftable library via `stack_check_addition()`.

Interestingly, the code in the reftable library is inferior compared to
the generic function:

  - It is slower than `refs_verify_refname_available()`, even though
    this can probably be optimized.

  - It does not provide a proper error message to the caller, and thus
    all the user would see is a generic "file/directory conflict"
    message.

Disable the D/F conflict checks in the reftable library by setting the
`skip_name_check` write option. This results in a non-negligible speedup
when writing many refs. The following benchmark writes 100k refs in a
single transaction:

  Benchmark 1: update-ref: create many refs (HEAD~)
    Time (mean ± σ):      3.241 s ±  0.040 s    [User: 1.854 s, System: 1.381 s]
    Range (min … max):    3.185 s …  3.454 s    100 runs

  Benchmark 2: update-ref: create many refs (HEAD)
    Time (mean ± σ):      2.878 s ±  0.024 s    [User: 1.506 s, System: 1.367 s]
    Range (min … max):    2.838 s …  2.960 s    100 runs

  Summary
    update-ref: create many refs (HEAD~) ran
      1.13 ± 0.02 times faster than update-ref: create many refs (HEAD)

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 refs/reftable-backend.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 8a54b0d8b2..7515dd3019 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -247,6 +247,11 @@ static struct ref_store *reftable_be_init(struct repository *repo,
 	refs->write_options.block_size = 4096;
 	refs->write_options.hash_id = repo->hash_algo->format_id;
 	refs->write_options.default_permissions = calc_shared_perm(0666 & ~mask);
+	/*
+	 * We verify names via `refs_verify_refname_available()`, so there is
+	 * no need to do the same checks in the reftable library again.
+	 */
+	refs->write_options.skip_name_check = 1;
 
 	/*
 	 * Set up the main reftable stack that is hosted in GIT_COMMON_DIR.
-- 
2.44.GIT


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[PATCH 4/9] refs/reftable: don't recompute committer ident

[Patrick Steinhardt]

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In order to write reflog entries we need to compute the committer's
identity as it becomes encoded in the log record itself. In the reftable
backend, computing the identity is repeated for every single reflog
entry which we are about to write in a transaction. Needless to say,
this can be quite a waste of effort when writing many refs with reflog
entries in a single transaction.

Refactor the code to pre-compute the committer information. This results
in a small speedup when writing 100000 refs in a single transaction:

  Benchmark 1: update-ref: create many refs (HEAD~)
    Time (mean ± σ):      2.895 s ±  0.020 s    [User: 1.516 s, System: 1.374 s]
    Range (min … max):    2.868 s …  2.983 s    100 runs

  Benchmark 2: update-ref: create many refs (HEAD)
    Time (mean ± σ):      2.845 s ±  0.017 s    [User: 1.461 s, System: 1.379 s]
    Range (min … max):    2.803 s …  2.913 s    100 runs

  Summary
    update-ref: create many refs (HEAD) ran
      1.02 ± 0.01 times faster than update-ref: create many refs (HEAD~)

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 refs/reftable-backend.c | 52 +++++++++++++++++++++++++++--------------
 1 file changed, 34 insertions(+), 18 deletions(-)

diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 7515dd3019..9e8967e82f 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -171,32 +171,30 @@ static int should_write_log(struct ref_store *refs, const char *refname)
 	}
 }
 
-static void fill_reftable_log_record(struct reftable_log_record *log)
+static void fill_reftable_log_record(struct reftable_log_record *log, const struct ident_split *split)
 {
-	const char *info = git_committer_info(0);
-	struct ident_split split = {0};
+	const char *tz_begin;
 	int sign = 1;
 
-	if (split_ident_line(&split, info, strlen(info)))
-		BUG("failed splitting committer info");
-
 	reftable_log_record_release(log);
 	log->value_type = REFTABLE_LOG_UPDATE;
 	log->value.update.name =
-		xstrndup(split.name_begin, split.name_end - split.name_begin);
+		xstrndup(split->name_begin, split->name_end - split->name_begin);
 	log->value.update.email =
-		xstrndup(split.mail_begin, split.mail_end - split.mail_begin);
-	log->value.update.time = atol(split.date_begin);
-	if (*split.tz_begin == '-') {
+		xstrndup(split->mail_begin, split->mail_end - split->mail_begin);
+	log->value.update.time = atol(split->date_begin);
+
+	tz_begin = split->tz_begin;
+	if (*tz_begin == '-') {
 		sign = -1;
-		split.tz_begin++;
+		tz_begin++;
 	}
-	if (*split.tz_begin == '+') {
+	if (*tz_begin == '+') {
 		sign = 1;
-		split.tz_begin++;
+		tz_begin++;
 	}
 
-	log->value.update.tz_offset = sign * atoi(split.tz_begin);
+	log->value.update.tz_offset = sign * atoi(tz_begin);
 }
 
 static int read_ref_without_reload(struct reftable_stack *stack,
@@ -1023,9 +1021,15 @@ static int write_transaction_table(struct reftable_writer *writer, void *cb_data
 		reftable_stack_merged_table(arg->stack);
 	uint64_t ts = reftable_stack_next_update_index(arg->stack);
 	struct reftable_log_record *logs = NULL;
+	struct ident_split committer_ident = {0};
 	size_t logs_nr = 0, logs_alloc = 0, i;
+	const char *committer_info;
 	int ret = 0;
 
+	committer_info = git_committer_info(0);
+	if (split_ident_line(&committer_ident, committer_info, strlen(committer_info)))
+		BUG("failed splitting committer info");
+
 	QSORT(arg->updates, arg->updates_nr, transaction_update_cmp);
 
 	reftable_writer_set_limits(writer, ts, ts);
@@ -1091,7 +1095,7 @@ static int write_transaction_table(struct reftable_writer *writer, void *cb_data
 			log = &logs[logs_nr++];
 			memset(log, 0, sizeof(*log));
 
-			fill_reftable_log_record(log);
+			fill_reftable_log_record(log, &committer_ident);
 			log->update_index = ts;
 			log->refname = xstrdup(u->refname);
 			memcpy(log->value.update.new_hash, u->new_oid.hash, GIT_MAX_RAWSZ);
@@ -1238,9 +1242,11 @@ static int write_create_symref_table(struct reftable_writer *writer, void *cb_da
 		.value.symref = (char *)create->target,
 		.update_index = ts,
 	};
+	struct ident_split committer_ident = {0};
 	struct reftable_log_record log = {0};
 	struct object_id new_oid;
 	struct object_id old_oid;
+	const char *committer_info;
 	int ret;
 
 	reftable_writer_set_limits(writer, ts, ts);
@@ -1268,7 +1274,11 @@ static int write_create_symref_table(struct reftable_writer *writer, void *cb_da
 	    !should_write_log(&create->refs->base, create->refname))
 		return 0;
 
-	fill_reftable_log_record(&log);
+	committer_info = git_committer_info(0);
+	if (split_ident_line(&committer_ident, committer_info, strlen(committer_info)))
+		BUG("failed splitting committer info");
+
+	fill_reftable_log_record(&log, &committer_ident);
 	log.refname = xstrdup(create->refname);
 	log.update_index = ts;
 	log.value.update.message = xstrndup(create->logmsg,
@@ -1344,10 +1354,16 @@ static int write_copy_table(struct reftable_writer *writer, void *cb_data)
 	struct reftable_log_record old_log = {0}, *logs = NULL;
 	struct reftable_iterator it = {0};
 	struct string_list skip = STRING_LIST_INIT_NODUP;
+	struct ident_split committer_ident = {0};
 	struct strbuf errbuf = STRBUF_INIT;
 	size_t logs_nr = 0, logs_alloc = 0, i;
+	const char *committer_info;
 	int ret;
 
+	committer_info = git_committer_info(0);
+	if (split_ident_line(&committer_ident, committer_info, strlen(committer_info)))
+		BUG("failed splitting committer info");
+
 	if (reftable_stack_read_ref(arg->stack, arg->oldname, &old_ref)) {
 		ret = error(_("refname %s not found"), arg->oldname);
 		goto done;
@@ -1422,7 +1438,7 @@ static int write_copy_table(struct reftable_writer *writer, void *cb_data)
 
 		ALLOC_GROW(logs, logs_nr + 1, logs_alloc);
 		memset(&logs[logs_nr], 0, sizeof(logs[logs_nr]));
-		fill_reftable_log_record(&logs[logs_nr]);
+		fill_reftable_log_record(&logs[logs_nr], &committer_ident);
 		logs[logs_nr].refname = (char *)arg->newname;
 		logs[logs_nr].update_index = deletion_ts;
 		logs[logs_nr].value.update.message =
@@ -1454,7 +1470,7 @@ static int write_copy_table(struct reftable_writer *writer, void *cb_data)
 	 */
 	ALLOC_GROW(logs, logs_nr + 1, logs_alloc);
 	memset(&logs[logs_nr], 0, sizeof(logs[logs_nr]));
-	fill_reftable_log_record(&logs[logs_nr]);
+	fill_reftable_log_record(&logs[logs_nr], &committer_ident);
 	logs[logs_nr].refname = (char *)arg->newname;
 	logs[logs_nr].update_index = creation_ts;
 	logs[logs_nr].value.update.message =
-- 
2.44.GIT


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Re: [PATCH 4/9] refs/reftable: don't recompute committer ident

[Junio C Hamano]

Patrick Steinhardt <ps@pks.im> writes:

> In order to write reflog entries we need to compute the committer's
> identity as it becomes encoded in the log record itself. In the reftable
> backend, computing the identity is repeated for every single reflog
> entry which we are about to write in a transaction. Needless to say,
> this can be quite a waste of effort when writing many refs with reflog
> entries in a single transaction.

It would have been nice to mention which caller benefits from this
rewrite in the above.

There are four callers of the fill_reftable_log_record() function.
The patch moves the split_ident() call from the callee to these four
callers.  The write_transaction_table() function calls it in a loop,
which should give us a big boost.  For other three callers, they
call it at most twice (i.e. write_copy_table() when deleting the old
one), so their contribution to the boost should be minimal.

Makes sense.

Re: [PATCH 4/9] refs/reftable: don't recompute committer ident

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 1187 bytes --]

On Wed, Apr 03, 2024 at 11:58:36AM -0700, Junio C Hamano wrote:
> Patrick Steinhardt <ps@pks.im> writes:
> 
> > In order to write reflog entries we need to compute the committer's
> > identity as it becomes encoded in the log record itself. In the reftable
> > backend, computing the identity is repeated for every single reflog
> > entry which we are about to write in a transaction. Needless to say,
> > this can be quite a waste of effort when writing many refs with reflog
> > entries in a single transaction.
> 
> It would have been nice to mention which caller benefits from this
> rewrite in the above.
> 
> There are four callers of the fill_reftable_log_record() function.
> The patch moves the split_ident() call from the callee to these four
> callers.  The write_transaction_table() function calls it in a loop,
> which should give us a big boost.  For other three callers, they
> call it at most twice (i.e. write_copy_table() when deleting the old
> one), so their contribution to the boost should be minimal.
> 
> Makes sense.

I do say it by saying "write in a transaction", but I agree that this is
not exactly obvious. Will rephrase.

Patrick

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[PATCH 5/9] reftable/writer: refactorings for `writer_add_record()`

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 2566 bytes --]

Large parts of the reftable library do not conform to Git's typical code
style. Refactor `writer_add_record()` such that it conforms better to it
and add some documentation that explains some of its more intricate
behaviour.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 reftable/writer.c | 38 +++++++++++++++++++++++++++-----------
 1 file changed, 27 insertions(+), 11 deletions(-)

diff --git a/reftable/writer.c b/reftable/writer.c
index 1d9ff0fbfa..0ad5eb8887 100644
--- a/reftable/writer.c
+++ b/reftable/writer.c
@@ -209,7 +209,8 @@ static int writer_add_record(struct reftable_writer *w,
 			     struct reftable_record *rec)
 {
 	struct strbuf key = STRBUF_INIT;
-	int err = -1;
+	int err;
+
 	reftable_record_key(rec, &key);
 	if (strbuf_cmp(&w->last_key, &key) >= 0) {
 		err = REFTABLE_API_ERROR;
@@ -218,27 +219,42 @@ static int writer_add_record(struct reftable_writer *w,
 
 	strbuf_reset(&w->last_key);
 	strbuf_addbuf(&w->last_key, &key);
-	if (!w->block_writer) {
+	if (!w->block_writer)
 		writer_reinit_block_writer(w, reftable_record_type(rec));
-	}
 
-	assert(block_writer_type(w->block_writer) == reftable_record_type(rec));
+	if (block_writer_type(w->block_writer) != reftable_record_type(rec))
+		BUG("record of type %d added to writer of type %d",
+		    reftable_record_type(rec), block_writer_type(w->block_writer));
 
-	if (block_writer_add(w->block_writer, rec) == 0) {
+	/*
+	 * Try to add the record to the writer. If this succeeds then we're
+	 * done. Otherwise the block writer may have hit the block size limit
+	 * and needs to be flushed.
+	 */
+	if (!block_writer_add(w->block_writer, rec)) {
 		err = 0;
 		goto done;
 	}
 
+	/*
+	 * The current block is full, so we need to flush and reinitialize the
+	 * writer to start writing the next block.
+	 */
 	err = writer_flush_block(w);
-	if (err < 0) {
+	if (err < 0)
 		goto done;
-	}
-
 	writer_reinit_block_writer(w, reftable_record_type(rec));
+
+	/*
+	 * Try to add the record to the writer again. If this still fails then
+	 * the record does not fit into the block size.
+	 *
+	 * TODO: it would be great to have `block_writer_add()` return proper
+	 *       error codes so that we don't have to second-guess the failure
+	 *       mode here.
+	 */
 	err = block_writer_add(w->block_writer, rec);
-	if (err == -1) {
-		/* we are writing into memory, so an error can only mean it
-		 * doesn't fit. */
+	if (err) {
 		err = REFTABLE_ENTRY_TOO_BIG_ERROR;
 		goto done;
 	}
-- 
2.44.GIT


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[PATCH 6/9] reftable/writer: refactorings for `writer_flush_nonempty_block()`

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 3749 bytes --]

Large parts of the reftable library do not conform to Git's typical code
style. Refactor `writer_flush_nonempty_block()` such that it conforms
better to it and add some documentation that explains some of its more
intricate behaviour.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 reftable/writer.c | 72 +++++++++++++++++++++++++++++------------------
 1 file changed, 44 insertions(+), 28 deletions(-)

diff --git a/reftable/writer.c b/reftable/writer.c
index 0ad5eb8887..d347ec4cc6 100644
--- a/reftable/writer.c
+++ b/reftable/writer.c
@@ -659,58 +659,74 @@ static void writer_clear_index(struct reftable_writer *w)
 	w->index_cap = 0;
 }
 
-static const int debug = 0;
-
 static int writer_flush_nonempty_block(struct reftable_writer *w)
 {
+	struct reftable_index_record index_record = {
+		.last_key = STRBUF_INIT,
+	};
 	uint8_t typ = block_writer_type(w->block_writer);
-	struct reftable_block_stats *bstats =
-		writer_reftable_block_stats(w, typ);
-	uint64_t block_typ_off = (bstats->blocks == 0) ? w->next : 0;
-	int raw_bytes = block_writer_finish(w->block_writer);
-	int padding = 0;
-	int err = 0;
-	struct reftable_index_record ir = { .last_key = STRBUF_INIT };
+	struct reftable_block_stats *bstats;
+	int raw_bytes, padding = 0, err;
+	uint64_t block_typ_off;
+
+	/*
+	 * Finish the current block. This will cause the block writer to emit
+	 * restart points and potentially compress records in case we are
+	 * writing a log block.
+	 *
+	 * Note that this is still happening in memory.
+	 */
+	raw_bytes = block_writer_finish(w->block_writer);
 	if (raw_bytes < 0)
 		return raw_bytes;
 
-	if (!w->opts.unpadded && typ != BLOCK_TYPE_LOG) {
+	/*
+	 * By default, all records except for log records are padded to the
+	 * block size.
+	 */
+	if (!w->opts.unpadded && typ != BLOCK_TYPE_LOG)
 		padding = w->opts.block_size - raw_bytes;
-	}
 
-	if (block_typ_off > 0) {
+	bstats = writer_reftable_block_stats(w, typ);
+	block_typ_off = (bstats->blocks == 0) ? w->next : 0;
+	if (block_typ_off > 0)
 		bstats->offset = block_typ_off;
-	}
-
 	bstats->entries += w->block_writer->entries;
 	bstats->restarts += w->block_writer->restart_len;
 	bstats->blocks++;
 	w->stats.blocks++;
 
-	if (debug) {
-		fprintf(stderr, "block %c off %" PRIu64 " sz %d (%d)\n", typ,
-			w->next, raw_bytes,
-			get_be24(w->block + w->block_writer->header_off + 1));
-	}
-
-	if (w->next == 0) {
+	/*
+	 * If this is the first block we're writing to the table then we need
+	 * to also write the reftable header.
+	 */
+	if (!w->next)
 		writer_write_header(w, w->block);
-	}
 
 	err = padded_write(w, w->block, raw_bytes, padding);
 	if (err < 0)
 		return err;
 
+	/*
+	 * Add an index record for every block that we're writing. If we end up
+	 * having more than a threshold of index records we will end up writing
+	 * an index section in `writer_finish_section()`. Each index record
+	 * contains the last record key of the block it is indexing as well as
+	 * the offset of that block.
+	 *
+	 * Note that this also applies when flushing index blocks, in which
+	 * case we will end up with a multi-level index.
+	 */
 	REFTABLE_ALLOC_GROW(w->index, w->index_len + 1, w->index_cap);
-
-	ir.offset = w->next;
-	strbuf_reset(&ir.last_key);
-	strbuf_addbuf(&ir.last_key, &w->block_writer->last_key);
-	w->index[w->index_len] = ir;
-
+	index_record.offset = w->next;
+	strbuf_reset(&index_record.last_key);
+	strbuf_addbuf(&index_record.last_key, &w->block_writer->last_key);
+	w->index[w->index_len] = index_record;
 	w->index_len++;
+
 	w->next += padding + raw_bytes;
 	w->block_writer = NULL;
+
 	return 0;
 }
 
-- 
2.44.GIT


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[PATCH 7/9] reftable/block: reuse zstream when writing log blocks

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 5605 bytes --]

While most reftable blocks are written to disk as-is, blocks for log
records are compressed with zlib. To compress them we use `compress2()`,
which is a simple wrapper around the more complex `zstream` interface
that would require multiple function invocations.

One downside of this interface is that `compress2()` will reallocate
internal state of the `zstream` interface on every single invocation.
Consequently, as we call `compress2()` for every single log block which
we are about to write, this can lead to quite some memory allocation
churn.

Refactor the code so that the block writer reuses a `zstream`. This
significantly reduces the number of bytes allocated when writing many
refs in a single transaction, as demonstrated by the following benchmark
that writes 100k refs in a single transaction.

Before:

  HEAP SUMMARY:
      in use at exit: 671,931 bytes in 151 blocks
    total heap usage: 22,631,887 allocs, 22,631,736 frees, 1,854,670,793 bytes allocated

After:

  HEAP SUMMARY:
      in use at exit: 671,931 bytes in 151 blocks
    total heap usage: 22,620,528 allocs, 22,620,377 frees, 1,245,549,984 bytes allocated

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 reftable/block.c  | 83 +++++++++++++++++++++++++++++++----------------
 reftable/block.h  |  1 +
 reftable/writer.c |  4 +++
 3 files changed, 60 insertions(+), 28 deletions(-)

diff --git a/reftable/block.c b/reftable/block.c
index e2a2cee58d..1fa74d418f 100644
--- a/reftable/block.c
+++ b/reftable/block.c
@@ -76,6 +76,10 @@ void block_writer_init(struct block_writer *bw, uint8_t typ, uint8_t *buf,
 	bw->entries = 0;
 	bw->restart_len = 0;
 	bw->last_key.len = 0;
+	if (!bw->zstream) {
+		REFTABLE_CALLOC_ARRAY(bw->zstream, 1);
+		deflateInit(bw->zstream, 9);
+	}
 }
 
 uint8_t block_writer_type(struct block_writer *bw)
@@ -139,39 +143,60 @@ int block_writer_finish(struct block_writer *w)
 	w->next += 2;
 	put_be24(w->buf + 1 + w->header_off, w->next);
 
+	/*
+	 * Log records are stored zlib-compressed. Note that the compression
+	 * also spans over the restart points we have just written.
+	 */
 	if (block_writer_type(w) == BLOCK_TYPE_LOG) {
 		int block_header_skip = 4 + w->header_off;
-		uLongf src_len = w->next - block_header_skip;
-		uLongf dest_cap = src_len * 1.001 + 12;
-		uint8_t *compressed;
-
-		REFTABLE_ALLOC_ARRAY(compressed, dest_cap);
-
-		while (1) {
-			uLongf out_dest_len = dest_cap;
-			int zresult = compress2(compressed, &out_dest_len,
-						w->buf + block_header_skip,
-						src_len, 9);
-			if (zresult == Z_BUF_ERROR && dest_cap < LONG_MAX) {
-				dest_cap *= 2;
-				compressed =
-					reftable_realloc(compressed, dest_cap);
-				if (compressed)
-					continue;
-			}
-
-			if (Z_OK != zresult) {
-				reftable_free(compressed);
-				return REFTABLE_ZLIB_ERROR;
-			}
-
-			memcpy(w->buf + block_header_skip, compressed,
-			       out_dest_len);
-			w->next = out_dest_len + block_header_skip;
+		uLongf src_len = w->next - block_header_skip, compressed_len;
+		unsigned char *compressed;
+		int ret;
+
+		ret = deflateReset(w->zstream);
+		if (ret != Z_OK)
+			return REFTABLE_ZLIB_ERROR;
+
+		/*
+		 * Precompute the upper bound of how many bytes the compressed
+		 * data may end up with. Combined with `Z_FINISH`, `deflate()`
+		 * is guaranteed to return `Z_STREAM_END`.
+		 */
+		compressed_len = deflateBound(w->zstream, src_len);
+		REFTABLE_ALLOC_ARRAY(compressed, compressed_len);
+
+		w->zstream->next_out = compressed;
+		w->zstream->avail_out = compressed_len;
+		w->zstream->next_in = w->buf + block_header_skip;
+		w->zstream->avail_in = src_len;
+
+		/*
+		 * We want to perform all decompression in a single
+		 * step, which is why we can pass Z_FINISH here. Note
+		 * that both `Z_OK` and `Z_BUF_ERROR` indicate that we
+		 * need to retry according to documentation.
+		 *
+		 * If the call fails we retry with a bigger output
+		 * buffer.
+		 */
+		ret = deflate(w->zstream, Z_FINISH);
+		if (ret != Z_STREAM_END) {
 			reftable_free(compressed);
-			break;
+			return REFTABLE_ZLIB_ERROR;
 		}
+
+		/*
+		 * Overwrite the uncompressed data we have already written and
+		 * adjust the `next` pointer to point right after the
+		 * compressed data.
+		 */
+		memcpy(w->buf + block_header_skip, compressed,
+		       w->zstream->total_out);
+		w->next = w->zstream->total_out + block_header_skip;
+
+		reftable_free(compressed);
 	}
+
 	return w->next;
 }
 
@@ -425,6 +450,8 @@ int block_reader_seek(struct block_reader *br, struct block_iter *it,
 
 void block_writer_release(struct block_writer *bw)
 {
+	deflateEnd(bw->zstream);
+	FREE_AND_NULL(bw->zstream);
 	FREE_AND_NULL(bw->restarts);
 	strbuf_release(&bw->last_key);
 	/* the block is not owned. */
diff --git a/reftable/block.h b/reftable/block.h
index 47acc62c0a..1375957fc8 100644
--- a/reftable/block.h
+++ b/reftable/block.h
@@ -18,6 +18,7 @@ license that can be found in the LICENSE file or at
  * allocation overhead.
  */
 struct block_writer {
+	z_stream *zstream;
 	uint8_t *buf;
 	uint32_t block_size;
 
diff --git a/reftable/writer.c b/reftable/writer.c
index d347ec4cc6..51e663bb19 100644
--- a/reftable/writer.c
+++ b/reftable/writer.c
@@ -153,6 +153,10 @@ void reftable_writer_free(struct reftable_writer *w)
 {
 	if (!w)
 		return;
+	if (w->block_writer) {
+		block_writer_release(w->block_writer);
+		w->block_writer = NULL;
+	}
 	reftable_free(w->block);
 	reftable_free(w);
 }
-- 
2.44.GIT


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Re: [PATCH 7/9] reftable/block: reuse zstream when writing log blocks

[Junio C Hamano]

Patrick Steinhardt <ps@pks.im> writes:

> @@ -139,39 +143,60 @@ int block_writer_finish(struct block_writer *w)
>  	w->next += 2;
>  	put_be24(w->buf + 1 + w->header_off, w->next);
>  
> +	/*
> +	 * Log records are stored zlib-compressed. Note that the compression
> +	 * also spans over the restart points we have just written.
> +	 */
>  	if (block_writer_type(w) == BLOCK_TYPE_LOG) {
>  		int block_header_skip = 4 + w->header_off;
> +		uLongf src_len = w->next - block_header_skip, compressed_len;
> +		unsigned char *compressed;
> +		int ret;
> +
> +		ret = deflateReset(w->zstream);
> +		if (ret != Z_OK)
> +			return REFTABLE_ZLIB_ERROR;
> +
> +		/*
> +		 * Precompute the upper bound of how many bytes the compressed
> +		 * data may end up with. Combined with `Z_FINISH`, `deflate()`
> +		 * is guaranteed to return `Z_STREAM_END`.
> +		 */
> +		compressed_len = deflateBound(w->zstream, src_len);
> +		REFTABLE_ALLOC_ARRAY(compressed, compressed_len);

OK.

> +		w->zstream->next_out = compressed;
> +		w->zstream->avail_out = compressed_len;
> +		w->zstream->next_in = w->buf + block_header_skip;
> +		w->zstream->avail_in = src_len;
> +
> +		/*
> +		 * We want to perform all decompression in a single
> +		 * step, which is why we can pass Z_FINISH here. Note
> +		 * that both `Z_OK` and `Z_BUF_ERROR` indicate that we
> +		 * need to retry according to documentation.
> +		 *
> +		 * If the call fails we retry with a bigger output
> +		 * buffer.
> +		 */

I am not sure where the retry is happening, though.

block_writer_finish() is called by writer_flush_nonempty_block()
which returns a negative return to its caller, which is
writer_flush_block().  writer_flush_block() in turn returns a
negative return to its callers from writer_add_record(),
write_finish_section(), and write_object_record().  Nobody seems to
react to REFTABLE_ZLIB_ERROR (other than the reftable/error.c that
stringifies the error for messages).

But we have asked deflateBound() so if we did not get Z_STREAM_END,
wouldn't it mean some data corruption that retrying would not help?

> +		ret = deflate(w->zstream, Z_FINISH);
> +		if (ret != Z_STREAM_END) {
>  			reftable_free(compressed);
> -			break;
> +			return REFTABLE_ZLIB_ERROR;
>  		}
> +
> +		/*
> +		 * Overwrite the uncompressed data we have already written and
> +		 * adjust the `next` pointer to point right after the
> +		 * compressed data.
> +		 */
> +		memcpy(w->buf + block_header_skip, compressed,
> +		       w->zstream->total_out);
> +		w->next = w->zstream->total_out + block_header_skip;
> +
> +		reftable_free(compressed);
>  	}
> +
>  	return w->next;
>  }

OK.

> @@ -425,6 +450,8 @@ int block_reader_seek(struct block_reader *br, struct block_iter *it,
>  
>  void block_writer_release(struct block_writer *bw)
>  {
> +	deflateEnd(bw->zstream);
> +	FREE_AND_NULL(bw->zstream);
>  	FREE_AND_NULL(bw->restarts);
>  	strbuf_release(&bw->last_key);
>  	/* the block is not owned. */
> diff --git a/reftable/block.h b/reftable/block.h
> index 47acc62c0a..1375957fc8 100644
> --- a/reftable/block.h
> +++ b/reftable/block.h
> @@ -18,6 +18,7 @@ license that can be found in the LICENSE file or at
>   * allocation overhead.
>   */
>  struct block_writer {
> +	z_stream *zstream;
>  	uint8_t *buf;
>  	uint32_t block_size;
>  
> diff --git a/reftable/writer.c b/reftable/writer.c
> index d347ec4cc6..51e663bb19 100644
> --- a/reftable/writer.c
> +++ b/reftable/writer.c
> @@ -153,6 +153,10 @@ void reftable_writer_free(struct reftable_writer *w)
>  {
>  	if (!w)
>  		return;
> +	if (w->block_writer) {
> +		block_writer_release(w->block_writer);
> +		w->block_writer = NULL;
> +	}

This smells like an orthogonal fix to an unrelated resource leakage?

>  	reftable_free(w->block);
>  	reftable_free(w);
>  }

Thanks.

Re: [PATCH 7/9] reftable/block: reuse zstream when writing log blocks

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 4421 bytes --]

On Wed, Apr 03, 2024 at 12:35:22PM -0700, Junio C Hamano wrote:
> Patrick Steinhardt <ps@pks.im> writes:
> 
> > @@ -139,39 +143,60 @@ int block_writer_finish(struct block_writer *w)
> >  	w->next += 2;
> >  	put_be24(w->buf + 1 + w->header_off, w->next);
> >  
> > +	/*
> > +	 * Log records are stored zlib-compressed. Note that the compression
> > +	 * also spans over the restart points we have just written.
> > +	 */
> >  	if (block_writer_type(w) == BLOCK_TYPE_LOG) {
> >  		int block_header_skip = 4 + w->header_off;
> > +		uLongf src_len = w->next - block_header_skip, compressed_len;
> > +		unsigned char *compressed;
> > +		int ret;
> > +
> > +		ret = deflateReset(w->zstream);
> > +		if (ret != Z_OK)
> > +			return REFTABLE_ZLIB_ERROR;
> > +
> > +		/*
> > +		 * Precompute the upper bound of how many bytes the compressed
> > +		 * data may end up with. Combined with `Z_FINISH`, `deflate()`
> > +		 * is guaranteed to return `Z_STREAM_END`.
> > +		 */
> > +		compressed_len = deflateBound(w->zstream, src_len);
> > +		REFTABLE_ALLOC_ARRAY(compressed, compressed_len);
> 
> OK.
> 
> > +		w->zstream->next_out = compressed;
> > +		w->zstream->avail_out = compressed_len;
> > +		w->zstream->next_in = w->buf + block_header_skip;
> > +		w->zstream->avail_in = src_len;
> > +
> > +		/*
> > +		 * We want to perform all decompression in a single
> > +		 * step, which is why we can pass Z_FINISH here. Note
> > +		 * that both `Z_OK` and `Z_BUF_ERROR` indicate that we
> > +		 * need to retry according to documentation.
> > +		 *
> > +		 * If the call fails we retry with a bigger output
> > +		 * buffer.
> > +		 */
> 
> I am not sure where the retry is happening, though.
> 
> block_writer_finish() is called by writer_flush_nonempty_block()
> which returns a negative return to its caller, which is
> writer_flush_block().  writer_flush_block() in turn returns a
> negative return to its callers from writer_add_record(),
> write_finish_section(), and write_object_record().  Nobody seems to
> react to REFTABLE_ZLIB_ERROR (other than the reftable/error.c that
> stringifies the error for messages).
> 
> But we have asked deflateBound() so if we did not get Z_STREAM_END,
> wouldn't it mean some data corruption that retrying would not help?

Yeha, this comment is stale from a previous iteration.

> > +		ret = deflate(w->zstream, Z_FINISH);
> > +		if (ret != Z_STREAM_END) {
> >  			reftable_free(compressed);
> > -			break;
> > +			return REFTABLE_ZLIB_ERROR;
> >  		}
> > +
> > +		/*
> > +		 * Overwrite the uncompressed data we have already written and
> > +		 * adjust the `next` pointer to point right after the
> > +		 * compressed data.
> > +		 */
> > +		memcpy(w->buf + block_header_skip, compressed,
> > +		       w->zstream->total_out);
> > +		w->next = w->zstream->total_out + block_header_skip;
> > +
> > +		reftable_free(compressed);
> >  	}
> > +
> >  	return w->next;
> >  }
> 
> OK.
> 
> > @@ -425,6 +450,8 @@ int block_reader_seek(struct block_reader *br, struct block_iter *it,
> >  
> >  void block_writer_release(struct block_writer *bw)
> >  {
> > +	deflateEnd(bw->zstream);
> > +	FREE_AND_NULL(bw->zstream);
> >  	FREE_AND_NULL(bw->restarts);
> >  	strbuf_release(&bw->last_key);
> >  	/* the block is not owned. */
> > diff --git a/reftable/block.h b/reftable/block.h
> > index 47acc62c0a..1375957fc8 100644
> > --- a/reftable/block.h
> > +++ b/reftable/block.h
> > @@ -18,6 +18,7 @@ license that can be found in the LICENSE file or at
> >   * allocation overhead.
> >   */
> >  struct block_writer {
> > +	z_stream *zstream;
> >  	uint8_t *buf;
> >  	uint32_t block_size;
> >  
> > diff --git a/reftable/writer.c b/reftable/writer.c
> > index d347ec4cc6..51e663bb19 100644
> > --- a/reftable/writer.c
> > +++ b/reftable/writer.c
> > @@ -153,6 +153,10 @@ void reftable_writer_free(struct reftable_writer *w)
> >  {
> >  	if (!w)
> >  		return;
> > +	if (w->block_writer) {
> > +		block_writer_release(w->block_writer);
> > +		w->block_writer = NULL;
> > +	}
> 
> This smells like an orthogonal fix to an unrelated resource leakage?

True. The memory leak simply never occurred before this change, but in
theory it could have happened. Will move into a separate commit.

Patrick

> >  	reftable_free(w->block);
> >  	reftable_free(w);
> >  }
> 
> Thanks.

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[PATCH 8/9] reftable/block: reuse compressed array

[Patrick Steinhardt]

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Similar to the preceding commit, let's reuse the `compressed` array that
we use to store compressed data in. This results in a small reduction in
memory allocations when writing many refs.

Before:

  HEAP SUMMARY:
      in use at exit: 671,931 bytes in 151 blocks
    total heap usage: 22,620,528 allocs, 22,620,377 frees, 1,245,549,984 bytes allocated

After:

  HEAP SUMMARY:
      in use at exit: 671,931 bytes in 151 blocks
    total heap usage: 22,618,257 allocs, 22,618,106 frees, 1,236,351,528 bytes allocated

So while the reduction in allocations isn't really all that big, it's a
low hanging fruit and thus there isn't much of a reason not to pick it.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 reftable/block.c | 14 +++++---------
 reftable/block.h |  3 +++
 2 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/reftable/block.c b/reftable/block.c
index 1fa74d418f..870d88b58d 100644
--- a/reftable/block.c
+++ b/reftable/block.c
@@ -150,7 +150,6 @@ int block_writer_finish(struct block_writer *w)
 	if (block_writer_type(w) == BLOCK_TYPE_LOG) {
 		int block_header_skip = 4 + w->header_off;
 		uLongf src_len = w->next - block_header_skip, compressed_len;
-		unsigned char *compressed;
 		int ret;
 
 		ret = deflateReset(w->zstream);
@@ -163,9 +162,9 @@ int block_writer_finish(struct block_writer *w)
 		 * is guaranteed to return `Z_STREAM_END`.
 		 */
 		compressed_len = deflateBound(w->zstream, src_len);
-		REFTABLE_ALLOC_ARRAY(compressed, compressed_len);
+		REFTABLE_ALLOC_GROW(w->compressed, compressed_len, w->compressed_cap);
 
-		w->zstream->next_out = compressed;
+		w->zstream->next_out = w->compressed;
 		w->zstream->avail_out = compressed_len;
 		w->zstream->next_in = w->buf + block_header_skip;
 		w->zstream->avail_in = src_len;
@@ -180,21 +179,17 @@ int block_writer_finish(struct block_writer *w)
 		 * buffer.
 		 */
 		ret = deflate(w->zstream, Z_FINISH);
-		if (ret != Z_STREAM_END) {
-			reftable_free(compressed);
+		if (ret != Z_STREAM_END)
 			return REFTABLE_ZLIB_ERROR;
-		}
 
 		/*
 		 * Overwrite the uncompressed data we have already written and
 		 * adjust the `next` pointer to point right after the
 		 * compressed data.
 		 */
-		memcpy(w->buf + block_header_skip, compressed,
+		memcpy(w->buf + block_header_skip, w->compressed,
 		       w->zstream->total_out);
 		w->next = w->zstream->total_out + block_header_skip;
-
-		reftable_free(compressed);
 	}
 
 	return w->next;
@@ -453,6 +448,7 @@ void block_writer_release(struct block_writer *bw)
 	deflateEnd(bw->zstream);
 	FREE_AND_NULL(bw->zstream);
 	FREE_AND_NULL(bw->restarts);
+	FREE_AND_NULL(bw->compressed);
 	strbuf_release(&bw->last_key);
 	/* the block is not owned. */
 }
diff --git a/reftable/block.h b/reftable/block.h
index 1375957fc8..657498014c 100644
--- a/reftable/block.h
+++ b/reftable/block.h
@@ -19,6 +19,9 @@ license that can be found in the LICENSE file or at
  */
 struct block_writer {
 	z_stream *zstream;
+	unsigned char *compressed;
+	size_t compressed_cap;
+
 	uint8_t *buf;
 	uint32_t block_size;
 
-- 
2.44.GIT


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[PATCH 9/9] reftable/writer: reset `last_key` instead of releasing it

[Patrick Steinhardt]

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The reftable writer tracks the last key that it has written so that it
can properly compute the compressed prefix for the next record it is
about to write. This last key must be reset whenever we move on to write
the next block, which is done in `writer_reinit_block_writer()`. We do
this by calling `strbuf_release()` though, which needlessly deallocates
the underlying buffer.

Convert the code to use `strbuf_reset()` instead, which saves one
allocation per block we're about to write. This requires us to also
amend `reftable_writer_free()` to release the buffer's memory now as we
previously seemingly relied on `writer_reinit_block_writer()` to release
the memory for us. Releasing memory here is the right thing to do
anyway.

While at it, convert a callsite where we truncate the buffer by setting
its length to zero to instead use `strbuf_reset()`, too.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 reftable/writer.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/reftable/writer.c b/reftable/writer.c
index 51e663bb19..4b3a4e3f3c 100644
--- a/reftable/writer.c
+++ b/reftable/writer.c
@@ -109,7 +109,7 @@ static void writer_reinit_block_writer(struct reftable_writer *w, uint8_t typ)
 		block_start = header_size(writer_version(w));
 	}
 
-	strbuf_release(&w->last_key);
+	strbuf_reset(&w->last_key);
 	block_writer_init(&w->block_writer_data, typ, w->block,
 			  w->opts.block_size, block_start,
 			  hash_size(w->opts.hash_id));
@@ -157,6 +157,7 @@ void reftable_writer_free(struct reftable_writer *w)
 		block_writer_release(w->block_writer);
 		w->block_writer = NULL;
 	}
+	strbuf_release(&w->last_key);
 	reftable_free(w->block);
 	reftable_free(w);
 }
@@ -472,7 +473,7 @@ static int writer_finish_section(struct reftable_writer *w)
 	bstats->max_index_level = max_level;
 
 	/* Reinit lastKey, as the next section can start with any key. */
-	w->last_key.len = 0;
+	strbuf_reset(&w->last_key);
 
 	return 0;
 }
-- 
2.44.GIT


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[PATCH v2 00/11] reftable: optimize write performance

[Patrick Steinhardt]

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Hi,

this is the second version of my patch series that aims to optimize
write performance in the reftable backend. I've made the following
changes compared to v2:

  - Added a new patch to drop "reftable/refname.{c,h}" and related
    completely.

  - Reworded the commit message for the committer ident refactorings.

  - Added a new patch that unifies the code paths that release reftable
    writer resources.

  - Fixed a stale comment claiming that we retry deflating, which we
    don't.

Thanks!

Patrick

Patrick Steinhardt (11):
  refs/reftable: fix D/F conflict error message on ref copy
  refs/reftable: perform explicit D/F check when writing symrefs
  refs/reftable: skip duplicate name checks
  reftable: remove name checks
  refs/reftable: don't recompute committer ident
  reftable/writer: refactorings for `writer_add_record()`
  reftable/writer: refactorings for `writer_flush_nonempty_block()`
  reftable/writer: unify releasing memory
  reftable/writer: reset `last_key` instead of releasing it
  reftable/block: reuse zstream when writing log blocks
  reftable/block: reuse compressed array

 Makefile                   |   2 -
 refs/reftable-backend.c    |  75 +++++++++----
 reftable/block.c           |  80 ++++++++------
 reftable/block.h           |   4 +
 reftable/error.c           |   2 -
 reftable/refname.c         | 209 -------------------------------------
 reftable/refname.h         |  29 -----
 reftable/refname_test.c    | 101 ------------------
 reftable/reftable-error.h  |   3 -
 reftable/reftable-tests.h  |   1 -
 reftable/reftable-writer.h |   4 -
 reftable/stack.c           |  67 +-----------
 reftable/stack_test.c      |  39 -------
 reftable/writer.c          | 137 +++++++++++++++---------
 t/helper/test-reftable.c   |   1 -
 t/t0610-reftable-basics.sh |  35 ++++++-
 16 files changed, 230 insertions(+), 559 deletions(-)
 delete mode 100644 reftable/refname.c
 delete mode 100644 reftable/refname.h
 delete mode 100644 reftable/refname_test.c

Range-diff against v1:
 1:  14b4dacd73 =  1:  926e802395 refs/reftable: fix D/F conflict error message on ref copy
 2:  55db366e61 =  2:  6190171906 refs/reftable: perform explicit D/F check when writing symrefs
 3:  ad8210ec65 =  3:  80008cc5e7 refs/reftable: skip duplicate name checks
 -:  ---------- >  4:  3497a570b4 reftable: remove name checks
 4:  a9a6795c02 !  5:  f892a3007b refs/reftable: don't recompute committer ident
    @@ Commit message
         refs/reftable: don't recompute committer ident
     
         In order to write reflog entries we need to compute the committer's
    -    identity as it becomes encoded in the log record itself. In the reftable
    -    backend, computing the identity is repeated for every single reflog
    -    entry which we are about to write in a transaction. Needless to say,
    -    this can be quite a waste of effort when writing many refs with reflog
    -    entries in a single transaction.
    +    identity as it gets encoded in the log record itself. The reftable
    +    backend does this via `git_committer_info()` and `split_ident_line()` in
    +    `fill_reftable_log_record()`, which use the Git config as well as
    +    environment variables to figure out the identity.
    +
    +    While most callers would only call `fill_reftable_log_record()` once or
    +    twice, `write_transaction_table()` will call it as many times as there
    +    are queued ref updates. This can be quite a waste of effort when writing
    +    many refs with reflog entries in a single transaction.
     
         Refactor the code to pre-compute the committer information. This results
         in a small speedup when writing 100000 refs in a single transaction:
 5:  8e9d69e9e6 =  6:  4877ab3921 reftable/writer: refactorings for `writer_add_record()`
 6:  1f903afdda =  7:  8f1c5b4169 reftable/writer: refactorings for `writer_flush_nonempty_block()`
 -:  ---------- >  8:  41db7414e1 reftable/writer: unify releasing memory
 9:  6950ae4ea7 !  9:  e5c7dbe417 reftable/writer: reset `last_key` instead of releasing it
    @@ reftable/writer.c: static void writer_reinit_block_writer(struct reftable_writer
      	block_writer_init(&w->block_writer_data, typ, w->block,
      			  w->opts.block_size, block_start,
      			  hash_size(w->opts.hash_id));
    -@@ reftable/writer.c: void reftable_writer_free(struct reftable_writer *w)
    - 		block_writer_release(w->block_writer);
    - 		w->block_writer = NULL;
    - 	}
    -+	strbuf_release(&w->last_key);
    - 	reftable_free(w->block);
    - 	reftable_free(w);
    - }
     @@ reftable/writer.c: static int writer_finish_section(struct reftable_writer *w)
      	bstats->max_index_level = max_level;
      
 7:  86dab54dfe ! 10:  26f422703f reftable/block: reuse zstream when writing log blocks
    @@ reftable/block.c: int block_writer_finish(struct block_writer *w)
     +		w->zstream->avail_in = src_len;
     +
     +		/*
    -+		 * We want to perform all decompression in a single
    -+		 * step, which is why we can pass Z_FINISH here. Note
    -+		 * that both `Z_OK` and `Z_BUF_ERROR` indicate that we
    -+		 * need to retry according to documentation.
    -+		 *
    -+		 * If the call fails we retry with a bigger output
    -+		 * buffer.
    ++		 * We want to perform all decompression in a single step, which
    ++		 * is why we can pass Z_FINISH here. As we have precomputed the
    ++		 * deflated buffer's size via `deflateBound()` this function is
    ++		 * guaranteed to succeed according to the zlib documentation.
     +		 */
     +		ret = deflate(w->zstream, Z_FINISH);
     +		if (ret != Z_STREAM_END) {
    @@ reftable/block.h: license that can be found in the LICENSE file or at
      	uint8_t *buf;
      	uint32_t block_size;
      
    -
    - ## reftable/writer.c ##
    -@@ reftable/writer.c: void reftable_writer_free(struct reftable_writer *w)
    - {
    - 	if (!w)
    - 		return;
    -+	if (w->block_writer) {
    -+		block_writer_release(w->block_writer);
    -+		w->block_writer = NULL;
    -+	}
    - 	reftable_free(w->block);
    - 	reftable_free(w);
    - }
 8:  9899b58dcf ! 11:  4f9df714da reftable/block: reuse compressed array
    @@ reftable/block.c: int block_writer_finish(struct block_writer *w)
      		w->zstream->next_in = w->buf + block_header_skip;
      		w->zstream->avail_in = src_len;
     @@ reftable/block.c: int block_writer_finish(struct block_writer *w)
    - 		 * buffer.
    + 		 * guaranteed to succeed according to the zlib documentation.
      		 */
      		ret = deflate(w->zstream, Z_FINISH);
     -		if (ret != Z_STREAM_END) {
-- 
2.44.GIT


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[PATCH v2 01/11] refs/reftable: fix D/F conflict error message on ref copy

[Patrick Steinhardt]

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The `write_copy_table()` function is shared between the reftable
implementations for renaming and copying refs. The only difference
between those two cases is that the rename will also delete the old
reference, whereas copying won't.

This has resulted in a bug though where we don't properly verify refname
availability. When calling `refs_verify_refname_available()`, we always
add the old ref name to the list of refs to be skipped when computing
availability, which indicates that the name would be available even if
it already exists at the current point in time. This is only the right
thing to do for renames though, not for copies.

The consequence of this bug is quite harmless because the reftable
backend has its own checks for D/F conflicts further down in the call
stack, and thus we refuse the update regardless of the bug. But all the
user gets in this case is an uninformative message that copying the ref
has failed, without any further details.

Fix the bug and only add the old name to the skip-list in case we rename
the ref. Consequently, this error case will now be handled by
`refs_verify_refname_available()`, which knows to provide a proper error
message.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 refs/reftable-backend.c    |  3 ++-
 t/t0610-reftable-basics.sh | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index e206d5a073..0358da14db 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -1351,7 +1351,8 @@ static int write_copy_table(struct reftable_writer *writer, void *cb_data)
 	/*
 	 * Verify that the new refname is available.
 	 */
-	string_list_insert(&skip, arg->oldname);
+	if (arg->delete_old)
+		string_list_insert(&skip, arg->oldname);
 	ret = refs_verify_refname_available(&arg->refs->base, arg->newname,
 					    NULL, &skip, &errbuf);
 	if (ret < 0) {
diff --git a/t/t0610-reftable-basics.sh b/t/t0610-reftable-basics.sh
index 686781192e..055231a707 100755
--- a/t/t0610-reftable-basics.sh
+++ b/t/t0610-reftable-basics.sh
@@ -730,6 +730,39 @@ test_expect_success 'reflog: updates via HEAD update HEAD reflog' '
 	)
 '
 
+test_expect_success 'branch: copying branch with D/F conflict' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit A &&
+		git branch branch &&
+		cat >expect <<-EOF &&
+		error: ${SQ}refs/heads/branch${SQ} exists; cannot create ${SQ}refs/heads/branch/moved${SQ}
+		fatal: branch copy failed
+		EOF
+		test_must_fail git branch -c branch branch/moved 2>err &&
+		test_cmp expect err
+	)
+'
+
+test_expect_success 'branch: moving branch with D/F conflict' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit A &&
+		git branch branch &&
+		git branch conflict &&
+		cat >expect <<-EOF &&
+		error: ${SQ}refs/heads/conflict${SQ} exists; cannot create ${SQ}refs/heads/conflict/moved${SQ}
+		fatal: branch rename failed
+		EOF
+		test_must_fail git branch -m branch conflict/moved 2>err &&
+		test_cmp expect err
+	)
+'
+
 test_expect_success 'worktree: adding worktree creates separate stack' '
 	test_when_finished "rm -rf repo worktree" &&
 	git init repo &&
-- 
2.44.GIT


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[PATCH v2 02/11] refs/reftable: perform explicit D/F check when writing symrefs

[Patrick Steinhardt]

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We already perform explicit D/F checks in all reftable callbacks which
write refs, except when writing symrefs. For one this leads to an error
message which isn't perfectly actionable because we only tell the user
that there was a D/F conflict, but not which refs conflicted with each
other. But second, once all ref updating callbacks explicitly check for
D/F conflicts, we can disable the D/F checks in the reftable library
itself and thus avoid some duplicated efforts.

Refactor the code that writes symref tables to explicitly call into
`refs_verify_refname_available()` when writing symrefs.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 refs/reftable-backend.c    | 20 +++++++++++++++++---
 t/t0610-reftable-basics.sh |  2 +-
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 0358da14db..8a54b0d8b2 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -1217,6 +1217,7 @@ static int reftable_be_pack_refs(struct ref_store *ref_store,
 struct write_create_symref_arg {
 	struct reftable_ref_store *refs;
 	struct reftable_stack *stack;
+	struct strbuf *err;
 	const char *refname;
 	const char *target;
 	const char *logmsg;
@@ -1239,6 +1240,11 @@ static int write_create_symref_table(struct reftable_writer *writer, void *cb_da
 
 	reftable_writer_set_limits(writer, ts, ts);
 
+	ret = refs_verify_refname_available(&create->refs->base, create->refname,
+					    NULL, NULL, create->err);
+	if (ret < 0)
+		return ret;
+
 	ret = reftable_writer_add_ref(writer, &ref);
 	if (ret)
 		return ret;
@@ -1280,12 +1286,14 @@ static int reftable_be_create_symref(struct ref_store *ref_store,
 	struct reftable_ref_store *refs =
 		reftable_be_downcast(ref_store, REF_STORE_WRITE, "create_symref");
 	struct reftable_stack *stack = stack_for(refs, refname, &refname);
+	struct strbuf err = STRBUF_INIT;
 	struct write_create_symref_arg arg = {
 		.refs = refs,
 		.stack = stack,
 		.refname = refname,
 		.target = target,
 		.logmsg = logmsg,
+		.err = &err,
 	};
 	int ret;
 
@@ -1301,9 +1309,15 @@ static int reftable_be_create_symref(struct ref_store *ref_store,
 
 done:
 	assert(ret != REFTABLE_API_ERROR);
-	if (ret)
-		error("unable to write symref for %s: %s", refname,
-		      reftable_error_str(ret));
+	if (ret) {
+		if (err.len)
+			error("%s", err.buf);
+		else
+			error("unable to write symref for %s: %s", refname,
+			      reftable_error_str(ret));
+	}
+
+	strbuf_release(&err);
 	return ret;
 }
 
diff --git a/t/t0610-reftable-basics.sh b/t/t0610-reftable-basics.sh
index 055231a707..12b0004781 100755
--- a/t/t0610-reftable-basics.sh
+++ b/t/t0610-reftable-basics.sh
@@ -255,7 +255,7 @@ test_expect_success 'ref transaction: creating symbolic ref fails with F/D confl
 	git init repo &&
 	test_commit -C repo A &&
 	cat >expect <<-EOF &&
-	error: unable to write symref for refs/heads: file/directory conflict
+	error: ${SQ}refs/heads/main${SQ} exists; cannot create ${SQ}refs/heads${SQ}
 	EOF
 	test_must_fail git -C repo symbolic-ref refs/heads refs/heads/foo 2>err &&
 	test_cmp expect err
-- 
2.44.GIT


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[PATCH v2 03/11] refs/reftable: skip duplicate name checks

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 2249 bytes --]

All the callback functions which write refs in the reftable backend
perform D/F conflict checks via `refs_verify_refname_available()`. But
in reality we perform these D/F conflict checks a second time in the
reftable library via `stack_check_addition()`.

Interestingly, the code in the reftable library is inferior compared to
the generic function:

  - It is slower than `refs_verify_refname_available()`, even though
    this can probably be optimized.

  - It does not provide a proper error message to the caller, and thus
    all the user would see is a generic "file/directory conflict"
    message.

Disable the D/F conflict checks in the reftable library by setting the
`skip_name_check` write option. This results in a non-negligible speedup
when writing many refs. The following benchmark writes 100k refs in a
single transaction:

  Benchmark 1: update-ref: create many refs (HEAD~)
    Time (mean ± σ):      3.241 s ±  0.040 s    [User: 1.854 s, System: 1.381 s]
    Range (min … max):    3.185 s …  3.454 s    100 runs

  Benchmark 2: update-ref: create many refs (HEAD)
    Time (mean ± σ):      2.878 s ±  0.024 s    [User: 1.506 s, System: 1.367 s]
    Range (min … max):    2.838 s …  2.960 s    100 runs

  Summary
    update-ref: create many refs (HEAD~) ran
      1.13 ± 0.02 times faster than update-ref: create many refs (HEAD)

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 refs/reftable-backend.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 8a54b0d8b2..7515dd3019 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -247,6 +247,11 @@ static struct ref_store *reftable_be_init(struct repository *repo,
 	refs->write_options.block_size = 4096;
 	refs->write_options.hash_id = repo->hash_algo->format_id;
 	refs->write_options.default_permissions = calc_shared_perm(0666 & ~mask);
+	/*
+	 * We verify names via `refs_verify_refname_available()`, so there is
+	 * no need to do the same checks in the reftable library again.
+	 */
+	refs->write_options.skip_name_check = 1;
 
 	/*
 	 * Set up the main reftable stack that is hosted in GIT_COMMON_DIR.
-- 
2.44.GIT


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[PATCH v2 04/11] reftable: remove name checks

[Patrick Steinhardt]

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In the preceding commit we have disabled name checks in the "reftable"
backend. These checks were responsible for verifying multiple things
when writing records to the reftable stack:

  - Detecting file/directory conflicts. Starting with the preceding
    commits this is now handled by the reftable backend itself via
    `refs_verify_refname_available()`.

  - Validating refnames. This is handled by `check_refname_format()` in
    the generic ref transacton layer.

The code in the reftable library is thus not used anymore and likely to
bitrot over time. Remove it.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 Makefile                   |   2 -
 refs/reftable-backend.c    |   5 -
 reftable/error.c           |   2 -
 reftable/refname.c         | 209 -------------------------------------
 reftable/refname.h         |  29 -----
 reftable/refname_test.c    | 101 ------------------
 reftable/reftable-error.h  |   3 -
 reftable/reftable-tests.h  |   1 -
 reftable/reftable-writer.h |   4 -
 reftable/stack.c           |  67 +-----------
 reftable/stack_test.c      |  39 -------
 t/helper/test-reftable.c   |   1 -
 12 files changed, 1 insertion(+), 462 deletions(-)
 delete mode 100644 reftable/refname.c
 delete mode 100644 reftable/refname.h
 delete mode 100644 reftable/refname_test.c

diff --git a/Makefile b/Makefile
index c43c1bd1a0..05e3d37581 100644
--- a/Makefile
+++ b/Makefile
@@ -2655,7 +2655,6 @@ REFTABLE_OBJS += reftable/merged.o
 REFTABLE_OBJS += reftable/pq.o
 REFTABLE_OBJS += reftable/reader.o
 REFTABLE_OBJS += reftable/record.o
-REFTABLE_OBJS += reftable/refname.o
 REFTABLE_OBJS += reftable/generic.o
 REFTABLE_OBJS += reftable/stack.o
 REFTABLE_OBJS += reftable/tree.o
@@ -2668,7 +2667,6 @@ REFTABLE_TEST_OBJS += reftable/merged_test.o
 REFTABLE_TEST_OBJS += reftable/pq_test.o
 REFTABLE_TEST_OBJS += reftable/record_test.o
 REFTABLE_TEST_OBJS += reftable/readwrite_test.o
-REFTABLE_TEST_OBJS += reftable/refname_test.o
 REFTABLE_TEST_OBJS += reftable/stack_test.o
 REFTABLE_TEST_OBJS += reftable/test_framework.o
 REFTABLE_TEST_OBJS += reftable/tree_test.o
diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 7515dd3019..8a54b0d8b2 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -247,11 +247,6 @@ static struct ref_store *reftable_be_init(struct repository *repo,
 	refs->write_options.block_size = 4096;
 	refs->write_options.hash_id = repo->hash_algo->format_id;
 	refs->write_options.default_permissions = calc_shared_perm(0666 & ~mask);
-	/*
-	 * We verify names via `refs_verify_refname_available()`, so there is
-	 * no need to do the same checks in the reftable library again.
-	 */
-	refs->write_options.skip_name_check = 1;
 
 	/*
 	 * Set up the main reftable stack that is hosted in GIT_COMMON_DIR.
diff --git a/reftable/error.c b/reftable/error.c
index 0d1766735e..169f89d2f1 100644
--- a/reftable/error.c
+++ b/reftable/error.c
@@ -27,8 +27,6 @@ const char *reftable_error_str(int err)
 		return "misuse of the reftable API";
 	case REFTABLE_ZLIB_ERROR:
 		return "zlib failure";
-	case REFTABLE_NAME_CONFLICT:
-		return "file/directory conflict";
 	case REFTABLE_EMPTY_TABLE_ERROR:
 		return "wrote empty table";
 	case REFTABLE_REFNAME_ERROR:
diff --git a/reftable/refname.c b/reftable/refname.c
deleted file mode 100644
index 7570e4acf9..0000000000
--- a/reftable/refname.c
+++ /dev/null
@@ -1,209 +0,0 @@
-/*
-  Copyright 2020 Google LLC
-
-  Use of this source code is governed by a BSD-style
-  license that can be found in the LICENSE file or at
-  https://developers.google.com/open-source/licenses/bsd
-*/
-
-#include "system.h"
-#include "reftable-error.h"
-#include "basics.h"
-#include "refname.h"
-#include "reftable-iterator.h"
-
-struct find_arg {
-	char **names;
-	const char *want;
-};
-
-static int find_name(size_t k, void *arg)
-{
-	struct find_arg *f_arg = arg;
-	return strcmp(f_arg->names[k], f_arg->want) >= 0;
-}
-
-static int modification_has_ref(struct modification *mod, const char *name)
-{
-	struct reftable_ref_record ref = { NULL };
-	int err = 0;
-
-	if (mod->add_len > 0) {
-		struct find_arg arg = {
-			.names = mod->add,
-			.want = name,
-		};
-		int idx = binsearch(mod->add_len, find_name, &arg);
-		if (idx < mod->add_len && !strcmp(mod->add[idx], name)) {
-			return 0;
-		}
-	}
-
-	if (mod->del_len > 0) {
-		struct find_arg arg = {
-			.names = mod->del,
-			.want = name,
-		};
-		int idx = binsearch(mod->del_len, find_name, &arg);
-		if (idx < mod->del_len && !strcmp(mod->del[idx], name)) {
-			return 1;
-		}
-	}
-
-	err = reftable_table_read_ref(&mod->tab, name, &ref);
-	reftable_ref_record_release(&ref);
-	return err;
-}
-
-static void modification_release(struct modification *mod)
-{
-	/* don't delete the strings themselves; they're owned by ref records.
-	 */
-	FREE_AND_NULL(mod->add);
-	FREE_AND_NULL(mod->del);
-	mod->add_len = 0;
-	mod->del_len = 0;
-}
-
-static int modification_has_ref_with_prefix(struct modification *mod,
-					    const char *prefix)
-{
-	struct reftable_iterator it = { NULL };
-	struct reftable_ref_record ref = { NULL };
-	int err = 0;
-
-	if (mod->add_len > 0) {
-		struct find_arg arg = {
-			.names = mod->add,
-			.want = prefix,
-		};
-		int idx = binsearch(mod->add_len, find_name, &arg);
-		if (idx < mod->add_len &&
-		    !strncmp(prefix, mod->add[idx], strlen(prefix)))
-			goto done;
-	}
-	err = reftable_table_seek_ref(&mod->tab, &it, prefix);
-	if (err)
-		goto done;
-
-	while (1) {
-		err = reftable_iterator_next_ref(&it, &ref);
-		if (err)
-			goto done;
-
-		if (mod->del_len > 0) {
-			struct find_arg arg = {
-				.names = mod->del,
-				.want = ref.refname,
-			};
-			int idx = binsearch(mod->del_len, find_name, &arg);
-			if (idx < mod->del_len &&
-			    !strcmp(ref.refname, mod->del[idx])) {
-				continue;
-			}
-		}
-
-		if (strncmp(ref.refname, prefix, strlen(prefix))) {
-			err = 1;
-			goto done;
-		}
-		err = 0;
-		goto done;
-	}
-
-done:
-	reftable_ref_record_release(&ref);
-	reftable_iterator_destroy(&it);
-	return err;
-}
-
-static int validate_refname(const char *name)
-{
-	while (1) {
-		char *next = strchr(name, '/');
-		if (!*name) {
-			return REFTABLE_REFNAME_ERROR;
-		}
-		if (!next) {
-			return 0;
-		}
-		if (next - name == 0 || (next - name == 1 && *name == '.') ||
-		    (next - name == 2 && name[0] == '.' && name[1] == '.'))
-			return REFTABLE_REFNAME_ERROR;
-		name = next + 1;
-	}
-	return 0;
-}
-
-int validate_ref_record_addition(struct reftable_table tab,
-				 struct reftable_ref_record *recs, size_t sz)
-{
-	struct modification mod = {
-		.tab = tab,
-		.add = reftable_calloc(sz, sizeof(*mod.add)),
-		.del = reftable_calloc(sz, sizeof(*mod.del)),
-	};
-	int i = 0;
-	int err = 0;
-	for (; i < sz; i++) {
-		if (reftable_ref_record_is_deletion(&recs[i])) {
-			mod.del[mod.del_len++] = recs[i].refname;
-		} else {
-			mod.add[mod.add_len++] = recs[i].refname;
-		}
-	}
-
-	err = modification_validate(&mod);
-	modification_release(&mod);
-	return err;
-}
-
-static void strbuf_trim_component(struct strbuf *sl)
-{
-	while (sl->len > 0) {
-		int is_slash = (sl->buf[sl->len - 1] == '/');
-		strbuf_setlen(sl, sl->len - 1);
-		if (is_slash)
-			break;
-	}
-}
-
-int modification_validate(struct modification *mod)
-{
-	struct strbuf slashed = STRBUF_INIT;
-	int err = 0;
-	int i = 0;
-	for (; i < mod->add_len; i++) {
-		err = validate_refname(mod->add[i]);
-		if (err)
-			goto done;
-		strbuf_reset(&slashed);
-		strbuf_addstr(&slashed, mod->add[i]);
-		strbuf_addstr(&slashed, "/");
-
-		err = modification_has_ref_with_prefix(mod, slashed.buf);
-		if (err == 0) {
-			err = REFTABLE_NAME_CONFLICT;
-			goto done;
-		}
-		if (err < 0)
-			goto done;
-
-		strbuf_reset(&slashed);
-		strbuf_addstr(&slashed, mod->add[i]);
-		while (slashed.len) {
-			strbuf_trim_component(&slashed);
-			err = modification_has_ref(mod, slashed.buf);
-			if (err == 0) {
-				err = REFTABLE_NAME_CONFLICT;
-				goto done;
-			}
-			if (err < 0)
-				goto done;
-		}
-	}
-	err = 0;
-done:
-	strbuf_release(&slashed);
-	return err;
-}
diff --git a/reftable/refname.h b/reftable/refname.h
deleted file mode 100644
index a24b40fcb4..0000000000
--- a/reftable/refname.h
+++ /dev/null
@@ -1,29 +0,0 @@
-/*
-  Copyright 2020 Google LLC
-
-  Use of this source code is governed by a BSD-style
-  license that can be found in the LICENSE file or at
-  https://developers.google.com/open-source/licenses/bsd
-*/
-#ifndef REFNAME_H
-#define REFNAME_H
-
-#include "reftable-record.h"
-#include "reftable-generic.h"
-
-struct modification {
-	struct reftable_table tab;
-
-	char **add;
-	size_t add_len;
-
-	char **del;
-	size_t del_len;
-};
-
-int validate_ref_record_addition(struct reftable_table tab,
-				 struct reftable_ref_record *recs, size_t sz);
-
-int modification_validate(struct modification *mod);
-
-#endif
diff --git a/reftable/refname_test.c b/reftable/refname_test.c
deleted file mode 100644
index b9cc62554e..0000000000
--- a/reftable/refname_test.c
+++ /dev/null
@@ -1,101 +0,0 @@
-/*
-Copyright 2020 Google LLC
-
-Use of this source code is governed by a BSD-style
-license that can be found in the LICENSE file or at
-https://developers.google.com/open-source/licenses/bsd
-*/
-
-#include "basics.h"
-#include "block.h"
-#include "blocksource.h"
-#include "reader.h"
-#include "record.h"
-#include "refname.h"
-#include "reftable-error.h"
-#include "reftable-writer.h"
-#include "system.h"
-
-#include "test_framework.h"
-#include "reftable-tests.h"
-
-struct testcase {
-	char *add;
-	char *del;
-	int error_code;
-};
-
-static void test_conflict(void)
-{
-	struct reftable_write_options opts = { 0 };
-	struct strbuf buf = STRBUF_INIT;
-	struct reftable_writer *w =
-		reftable_new_writer(&strbuf_add_void, &noop_flush, &buf, &opts);
-	struct reftable_ref_record rec = {
-		.refname = "a/b",
-		.value_type = REFTABLE_REF_SYMREF,
-		.value.symref = "destination", /* make sure it's not a symref.
-						*/
-		.update_index = 1,
-	};
-	int err;
-	int i;
-	struct reftable_block_source source = { NULL };
-	struct reftable_reader *rd = NULL;
-	struct reftable_table tab = { NULL };
-	struct testcase cases[] = {
-		{ "a/b/c", NULL, REFTABLE_NAME_CONFLICT },
-		{ "b", NULL, 0 },
-		{ "a", NULL, REFTABLE_NAME_CONFLICT },
-		{ "a", "a/b", 0 },
-
-		{ "p/", NULL, REFTABLE_REFNAME_ERROR },
-		{ "p//q", NULL, REFTABLE_REFNAME_ERROR },
-		{ "p/./q", NULL, REFTABLE_REFNAME_ERROR },
-		{ "p/../q", NULL, REFTABLE_REFNAME_ERROR },
-
-		{ "a/b/c", "a/b", 0 },
-		{ NULL, "a//b", 0 },
-	};
-	reftable_writer_set_limits(w, 1, 1);
-
-	err = reftable_writer_add_ref(w, &rec);
-	EXPECT_ERR(err);
-
-	err = reftable_writer_close(w);
-	EXPECT_ERR(err);
-	reftable_writer_free(w);
-
-	block_source_from_strbuf(&source, &buf);
-	err = reftable_new_reader(&rd, &source, "filename");
-	EXPECT_ERR(err);
-
-	reftable_table_from_reader(&tab, rd);
-
-	for (i = 0; i < ARRAY_SIZE(cases); i++) {
-		struct modification mod = {
-			.tab = tab,
-		};
-
-		if (cases[i].add) {
-			mod.add = &cases[i].add;
-			mod.add_len = 1;
-		}
-		if (cases[i].del) {
-			mod.del = &cases[i].del;
-			mod.del_len = 1;
-		}
-
-		err = modification_validate(&mod);
-		EXPECT(err == cases[i].error_code);
-	}
-
-	reftable_reader_free(rd);
-	strbuf_release(&buf);
-}
-
-int refname_test_main(int argc, const char *argv[])
-{
-	RUN_TEST(test_conflict);
-	return 0;
-}
diff --git a/reftable/reftable-error.h b/reftable/reftable-error.h
index 4c457aaaf8..3a5f5b92c6 100644
--- a/reftable/reftable-error.h
+++ b/reftable/reftable-error.h
@@ -48,9 +48,6 @@ enum reftable_error {
 	/* Wrote a table without blocks. */
 	REFTABLE_EMPTY_TABLE_ERROR = -8,
 
-	/* Dir/file conflict. */
-	REFTABLE_NAME_CONFLICT = -9,
-
 	/* Invalid ref name. */
 	REFTABLE_REFNAME_ERROR = -10,
 
diff --git a/reftable/reftable-tests.h b/reftable/reftable-tests.h
index 0019cbcfa4..114cc3d053 100644
--- a/reftable/reftable-tests.h
+++ b/reftable/reftable-tests.h
@@ -14,7 +14,6 @@ int block_test_main(int argc, const char **argv);
 int merged_test_main(int argc, const char **argv);
 int pq_test_main(int argc, const char **argv);
 int record_test_main(int argc, const char **argv);
-int refname_test_main(int argc, const char **argv);
 int readwrite_test_main(int argc, const char **argv);
 int stack_test_main(int argc, const char **argv);
 int tree_test_main(int argc, const char **argv);
diff --git a/reftable/reftable-writer.h b/reftable/reftable-writer.h
index 7c7cae5f99..3c119e2bbb 100644
--- a/reftable/reftable-writer.h
+++ b/reftable/reftable-writer.h
@@ -38,10 +38,6 @@ struct reftable_write_options {
 	/* Default mode for creating files. If unset, use 0666 (+umask) */
 	unsigned int default_permissions;
 
-	/* boolean: do not check ref names for validity or dir/file conflicts.
-	 */
-	unsigned skip_name_check : 1;
-
 	/* boolean: copy log messages exactly. If unset, check that the message
 	 *   is a single line, and add '\n' if missing.
 	 */
diff --git a/reftable/stack.c b/reftable/stack.c
index 1ecf1b9751..e264df5ced 100644
--- a/reftable/stack.c
+++ b/reftable/stack.c
@@ -12,8 +12,8 @@ license that can be found in the LICENSE file or at
 #include "system.h"
 #include "merged.h"
 #include "reader.h"
-#include "refname.h"
 #include "reftable-error.h"
+#include "reftable-generic.h"
 #include "reftable-record.h"
 #include "reftable-merged.h"
 #include "writer.h"
@@ -27,8 +27,6 @@ static int stack_write_compact(struct reftable_stack *st,
 			       struct reftable_writer *wr,
 			       size_t first, size_t last,
 			       struct reftable_log_expiry_config *config);
-static int stack_check_addition(struct reftable_stack *st,
-				const char *new_tab_name);
 static void reftable_addition_close(struct reftable_addition *add);
 static int reftable_stack_reload_maybe_reuse(struct reftable_stack *st,
 					     int reuse_open);
@@ -781,10 +779,6 @@ int reftable_addition_add(struct reftable_addition *add,
 		goto done;
 	}
 
-	err = stack_check_addition(add->stack, get_tempfile_path(tab_file));
-	if (err < 0)
-		goto done;
-
 	if (wr->min_update_index < add->next_update_index) {
 		err = REFTABLE_API_ERROR;
 		goto done;
@@ -1340,65 +1334,6 @@ int reftable_stack_read_log(struct reftable_stack *st, const char *refname,
 	return err;
 }
 
-static int stack_check_addition(struct reftable_stack *st,
-				const char *new_tab_name)
-{
-	int err = 0;
-	struct reftable_block_source src = { NULL };
-	struct reftable_reader *rd = NULL;
-	struct reftable_table tab = { NULL };
-	struct reftable_ref_record *refs = NULL;
-	struct reftable_iterator it = { NULL };
-	int cap = 0;
-	int len = 0;
-	int i = 0;
-
-	if (st->config.skip_name_check)
-		return 0;
-
-	err = reftable_block_source_from_file(&src, new_tab_name);
-	if (err < 0)
-		goto done;
-
-	err = reftable_new_reader(&rd, &src, new_tab_name);
-	if (err < 0)
-		goto done;
-
-	err = reftable_reader_seek_ref(rd, &it, "");
-	if (err > 0) {
-		err = 0;
-		goto done;
-	}
-	if (err < 0)
-		goto done;
-
-	while (1) {
-		struct reftable_ref_record ref = { NULL };
-		err = reftable_iterator_next_ref(&it, &ref);
-		if (err > 0)
-			break;
-		if (err < 0)
-			goto done;
-
-		REFTABLE_ALLOC_GROW(refs, len + 1, cap);
-		refs[len++] = ref;
-	}
-
-	reftable_table_from_merged_table(&tab, reftable_stack_merged_table(st));
-
-	err = validate_ref_record_addition(tab, refs, len);
-
-done:
-	for (i = 0; i < len; i++) {
-		reftable_ref_record_release(&refs[i]);
-	}
-
-	free(refs);
-	reftable_iterator_destroy(&it);
-	reftable_reader_free(rd);
-	return err;
-}
-
 static int is_table_name(const char *s)
 {
 	const char *dot = strrchr(s, '.');
diff --git a/reftable/stack_test.c b/reftable/stack_test.c
index 0dc9a44648..b88097c3b6 100644
--- a/reftable/stack_test.c
+++ b/reftable/stack_test.c
@@ -353,44 +353,6 @@ static void test_reftable_stack_transaction_api_performs_auto_compaction(void)
 	clear_dir(dir);
 }
 
-static void test_reftable_stack_validate_refname(void)
-{
-	struct reftable_write_options cfg = { 0 };
-	struct reftable_stack *st = NULL;
-	int err;
-	char *dir = get_tmp_dir(__LINE__);
-
-	int i;
-	struct reftable_ref_record ref = {
-		.refname = "a/b",
-		.update_index = 1,
-		.value_type = REFTABLE_REF_SYMREF,
-		.value.symref = "master",
-	};
-	char *additions[] = { "a", "a/b/c" };
-
-	err = reftable_new_stack(&st, dir, cfg);
-	EXPECT_ERR(err);
-
-	err = reftable_stack_add(st, &write_test_ref, &ref);
-	EXPECT_ERR(err);
-
-	for (i = 0; i < ARRAY_SIZE(additions); i++) {
-		struct reftable_ref_record ref = {
-			.refname = additions[i],
-			.update_index = 1,
-			.value_type = REFTABLE_REF_SYMREF,
-			.value.symref = "master",
-		};
-
-		err = reftable_stack_add(st, &write_test_ref, &ref);
-		EXPECT(err == REFTABLE_NAME_CONFLICT);
-	}
-
-	reftable_stack_destroy(st);
-	clear_dir(dir);
-}
-
 static int write_error(struct reftable_writer *wr, void *arg)
 {
 	return *((int *)arg);
@@ -1097,7 +1059,6 @@ int stack_test_main(int argc, const char *argv[])
 	RUN_TEST(test_reftable_stack_transaction_api_performs_auto_compaction);
 	RUN_TEST(test_reftable_stack_update_index_check);
 	RUN_TEST(test_reftable_stack_uptodate);
-	RUN_TEST(test_reftable_stack_validate_refname);
 	RUN_TEST(test_sizes_to_segments);
 	RUN_TEST(test_sizes_to_segments_all_equal);
 	RUN_TEST(test_sizes_to_segments_empty);
diff --git a/t/helper/test-reftable.c b/t/helper/test-reftable.c
index 00237ef0d9..bae731669c 100644
--- a/t/helper/test-reftable.c
+++ b/t/helper/test-reftable.c
@@ -13,7 +13,6 @@ int cmd__reftable(int argc, const char **argv)
 	readwrite_test_main(argc, argv);
 	merged_test_main(argc, argv);
 	stack_test_main(argc, argv);
-	refname_test_main(argc, argv);
 	return 0;
 }
 
-- 
2.44.GIT


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[PATCH v2 05/11] refs/reftable: don't recompute committer ident

[Patrick Steinhardt]

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In order to write reflog entries we need to compute the committer's
identity as it gets encoded in the log record itself. The reftable
backend does this via `git_committer_info()` and `split_ident_line()` in
`fill_reftable_log_record()`, which use the Git config as well as
environment variables to figure out the identity.

While most callers would only call `fill_reftable_log_record()` once or
twice, `write_transaction_table()` will call it as many times as there
are queued ref updates. This can be quite a waste of effort when writing
many refs with reflog entries in a single transaction.

Refactor the code to pre-compute the committer information. This results
in a small speedup when writing 100000 refs in a single transaction:

  Benchmark 1: update-ref: create many refs (HEAD~)
    Time (mean ± σ):      2.895 s ±  0.020 s    [User: 1.516 s, System: 1.374 s]
    Range (min … max):    2.868 s …  2.983 s    100 runs

  Benchmark 2: update-ref: create many refs (HEAD)
    Time (mean ± σ):      2.845 s ±  0.017 s    [User: 1.461 s, System: 1.379 s]
    Range (min … max):    2.803 s …  2.913 s    100 runs

  Summary
    update-ref: create many refs (HEAD) ran
      1.02 ± 0.01 times faster than update-ref: create many refs (HEAD~)

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 refs/reftable-backend.c | 52 +++++++++++++++++++++++++++--------------
 1 file changed, 34 insertions(+), 18 deletions(-)

diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 8a54b0d8b2..a5ef36ffa9 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -171,32 +171,30 @@ static int should_write_log(struct ref_store *refs, const char *refname)
 	}
 }
 
-static void fill_reftable_log_record(struct reftable_log_record *log)
+static void fill_reftable_log_record(struct reftable_log_record *log, const struct ident_split *split)
 {
-	const char *info = git_committer_info(0);
-	struct ident_split split = {0};
+	const char *tz_begin;
 	int sign = 1;
 
-	if (split_ident_line(&split, info, strlen(info)))
-		BUG("failed splitting committer info");
-
 	reftable_log_record_release(log);
 	log->value_type = REFTABLE_LOG_UPDATE;
 	log->value.update.name =
-		xstrndup(split.name_begin, split.name_end - split.name_begin);
+		xstrndup(split->name_begin, split->name_end - split->name_begin);
 	log->value.update.email =
-		xstrndup(split.mail_begin, split.mail_end - split.mail_begin);
-	log->value.update.time = atol(split.date_begin);
-	if (*split.tz_begin == '-') {
+		xstrndup(split->mail_begin, split->mail_end - split->mail_begin);
+	log->value.update.time = atol(split->date_begin);
+
+	tz_begin = split->tz_begin;
+	if (*tz_begin == '-') {
 		sign = -1;
-		split.tz_begin++;
+		tz_begin++;
 	}
-	if (*split.tz_begin == '+') {
+	if (*tz_begin == '+') {
 		sign = 1;
-		split.tz_begin++;
+		tz_begin++;
 	}
 
-	log->value.update.tz_offset = sign * atoi(split.tz_begin);
+	log->value.update.tz_offset = sign * atoi(tz_begin);
 }
 
 static int read_ref_without_reload(struct reftable_stack *stack,
@@ -1018,9 +1016,15 @@ static int write_transaction_table(struct reftable_writer *writer, void *cb_data
 		reftable_stack_merged_table(arg->stack);
 	uint64_t ts = reftable_stack_next_update_index(arg->stack);
 	struct reftable_log_record *logs = NULL;
+	struct ident_split committer_ident = {0};
 	size_t logs_nr = 0, logs_alloc = 0, i;
+	const char *committer_info;
 	int ret = 0;
 
+	committer_info = git_committer_info(0);
+	if (split_ident_line(&committer_ident, committer_info, strlen(committer_info)))
+		BUG("failed splitting committer info");
+
 	QSORT(arg->updates, arg->updates_nr, transaction_update_cmp);
 
 	reftable_writer_set_limits(writer, ts, ts);
@@ -1086,7 +1090,7 @@ static int write_transaction_table(struct reftable_writer *writer, void *cb_data
 			log = &logs[logs_nr++];
 			memset(log, 0, sizeof(*log));
 
-			fill_reftable_log_record(log);
+			fill_reftable_log_record(log, &committer_ident);
 			log->update_index = ts;
 			log->refname = xstrdup(u->refname);
 			memcpy(log->value.update.new_hash, u->new_oid.hash, GIT_MAX_RAWSZ);
@@ -1233,9 +1237,11 @@ static int write_create_symref_table(struct reftable_writer *writer, void *cb_da
 		.value.symref = (char *)create->target,
 		.update_index = ts,
 	};
+	struct ident_split committer_ident = {0};
 	struct reftable_log_record log = {0};
 	struct object_id new_oid;
 	struct object_id old_oid;
+	const char *committer_info;
 	int ret;
 
 	reftable_writer_set_limits(writer, ts, ts);
@@ -1263,7 +1269,11 @@ static int write_create_symref_table(struct reftable_writer *writer, void *cb_da
 	    !should_write_log(&create->refs->base, create->refname))
 		return 0;
 
-	fill_reftable_log_record(&log);
+	committer_info = git_committer_info(0);
+	if (split_ident_line(&committer_ident, committer_info, strlen(committer_info)))
+		BUG("failed splitting committer info");
+
+	fill_reftable_log_record(&log, &committer_ident);
 	log.refname = xstrdup(create->refname);
 	log.update_index = ts;
 	log.value.update.message = xstrndup(create->logmsg,
@@ -1339,10 +1349,16 @@ static int write_copy_table(struct reftable_writer *writer, void *cb_data)
 	struct reftable_log_record old_log = {0}, *logs = NULL;
 	struct reftable_iterator it = {0};
 	struct string_list skip = STRING_LIST_INIT_NODUP;
+	struct ident_split committer_ident = {0};
 	struct strbuf errbuf = STRBUF_INIT;
 	size_t logs_nr = 0, logs_alloc = 0, i;
+	const char *committer_info;
 	int ret;
 
+	committer_info = git_committer_info(0);
+	if (split_ident_line(&committer_ident, committer_info, strlen(committer_info)))
+		BUG("failed splitting committer info");
+
 	if (reftable_stack_read_ref(arg->stack, arg->oldname, &old_ref)) {
 		ret = error(_("refname %s not found"), arg->oldname);
 		goto done;
@@ -1417,7 +1433,7 @@ static int write_copy_table(struct reftable_writer *writer, void *cb_data)
 
 		ALLOC_GROW(logs, logs_nr + 1, logs_alloc);
 		memset(&logs[logs_nr], 0, sizeof(logs[logs_nr]));
-		fill_reftable_log_record(&logs[logs_nr]);
+		fill_reftable_log_record(&logs[logs_nr], &committer_ident);
 		logs[logs_nr].refname = (char *)arg->newname;
 		logs[logs_nr].update_index = deletion_ts;
 		logs[logs_nr].value.update.message =
@@ -1449,7 +1465,7 @@ static int write_copy_table(struct reftable_writer *writer, void *cb_data)
 	 */
 	ALLOC_GROW(logs, logs_nr + 1, logs_alloc);
 	memset(&logs[logs_nr], 0, sizeof(logs[logs_nr]));
-	fill_reftable_log_record(&logs[logs_nr]);
+	fill_reftable_log_record(&logs[logs_nr], &committer_ident);
 	logs[logs_nr].refname = (char *)arg->newname;
 	logs[logs_nr].update_index = creation_ts;
 	logs[logs_nr].value.update.message =
-- 
2.44.GIT


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[PATCH v2 06/11] reftable/writer: refactorings for `writer_add_record()`

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 2566 bytes --]

Large parts of the reftable library do not conform to Git's typical code
style. Refactor `writer_add_record()` such that it conforms better to it
and add some documentation that explains some of its more intricate
behaviour.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 reftable/writer.c | 38 +++++++++++++++++++++++++++-----------
 1 file changed, 27 insertions(+), 11 deletions(-)

diff --git a/reftable/writer.c b/reftable/writer.c
index 1d9ff0fbfa..0ad5eb8887 100644
--- a/reftable/writer.c
+++ b/reftable/writer.c
@@ -209,7 +209,8 @@ static int writer_add_record(struct reftable_writer *w,
 			     struct reftable_record *rec)
 {
 	struct strbuf key = STRBUF_INIT;
-	int err = -1;
+	int err;
+
 	reftable_record_key(rec, &key);
 	if (strbuf_cmp(&w->last_key, &key) >= 0) {
 		err = REFTABLE_API_ERROR;
@@ -218,27 +219,42 @@ static int writer_add_record(struct reftable_writer *w,
 
 	strbuf_reset(&w->last_key);
 	strbuf_addbuf(&w->last_key, &key);
-	if (!w->block_writer) {
+	if (!w->block_writer)
 		writer_reinit_block_writer(w, reftable_record_type(rec));
-	}
 
-	assert(block_writer_type(w->block_writer) == reftable_record_type(rec));
+	if (block_writer_type(w->block_writer) != reftable_record_type(rec))
+		BUG("record of type %d added to writer of type %d",
+		    reftable_record_type(rec), block_writer_type(w->block_writer));
 
-	if (block_writer_add(w->block_writer, rec) == 0) {
+	/*
+	 * Try to add the record to the writer. If this succeeds then we're
+	 * done. Otherwise the block writer may have hit the block size limit
+	 * and needs to be flushed.
+	 */
+	if (!block_writer_add(w->block_writer, rec)) {
 		err = 0;
 		goto done;
 	}
 
+	/*
+	 * The current block is full, so we need to flush and reinitialize the
+	 * writer to start writing the next block.
+	 */
 	err = writer_flush_block(w);
-	if (err < 0) {
+	if (err < 0)
 		goto done;
-	}
-
 	writer_reinit_block_writer(w, reftable_record_type(rec));
+
+	/*
+	 * Try to add the record to the writer again. If this still fails then
+	 * the record does not fit into the block size.
+	 *
+	 * TODO: it would be great to have `block_writer_add()` return proper
+	 *       error codes so that we don't have to second-guess the failure
+	 *       mode here.
+	 */
 	err = block_writer_add(w->block_writer, rec);
-	if (err == -1) {
-		/* we are writing into memory, so an error can only mean it
-		 * doesn't fit. */
+	if (err) {
 		err = REFTABLE_ENTRY_TOO_BIG_ERROR;
 		goto done;
 	}
-- 
2.44.GIT


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Re: [PATCH v2 06/11] reftable/writer: refactorings for `writer_add_record()`

[Han-Wen Nienhuys]

On Thu, Apr 4, 2024 at 7:48 AM Patrick Steinhardt <ps@pks.im> wrote:
> +       /*
> +        * Try to add the record to the writer again. If this still fails then
> +        * the record does not fit into the block size.
> +        *
> +        * TODO: it would be great to have `block_writer_add()` return proper
> +        *       error codes so that we don't have to second-guess the failure
> +        *       mode here.
> +        */

The Go code returns a (size, boolean) tuple for the write routines
here, but that does not really work in the Git C style.

If you make the routines return error codes it suggests that the
in-memory write can fail for other reasons beyond "does not fit". Not
sure if that is really an improvement.

-- 
Han-Wen Nienhuys - hanwenn@gmail.com - http://www.xs4all.nl/~hanwen

Re: [PATCH v2 06/11] reftable/writer: refactorings for `writer_add_record()`

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 1140 bytes --]

On Thu, Apr 04, 2024 at 08:58:08AM +0200, Han-Wen Nienhuys wrote:
> On Thu, Apr 4, 2024 at 7:48 AM Patrick Steinhardt <ps@pks.im> wrote:
> > +       /*
> > +        * Try to add the record to the writer again. If this still fails then
> > +        * the record does not fit into the block size.
> > +        *
> > +        * TODO: it would be great to have `block_writer_add()` return proper
> > +        *       error codes so that we don't have to second-guess the failure
> > +        *       mode here.
> > +        */
> 
> The Go code returns a (size, boolean) tuple for the write routines
> here, but that does not really work in the Git C style.
> 
> If you make the routines return error codes it suggests that the
> in-memory write can fail for other reasons beyond "does not fit". Not
> sure if that is really an improvement.

In reality, `block_writer_add()` already can fail because of different
reasons: it returns `REFTABLE_API_ERROR` if the passed-in record has an
empty key. This shouldn't ever happen, but it demonstrates that this is
certainly an area which needs some further cleanups.

Patrick

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[PATCH v2 07/11] reftable/writer: refactorings for `writer_flush_nonempty_block()`

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 3749 bytes --]

Large parts of the reftable library do not conform to Git's typical code
style. Refactor `writer_flush_nonempty_block()` such that it conforms
better to it and add some documentation that explains some of its more
intricate behaviour.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 reftable/writer.c | 72 +++++++++++++++++++++++++++++------------------
 1 file changed, 44 insertions(+), 28 deletions(-)

diff --git a/reftable/writer.c b/reftable/writer.c
index 0ad5eb8887..d347ec4cc6 100644
--- a/reftable/writer.c
+++ b/reftable/writer.c
@@ -659,58 +659,74 @@ static void writer_clear_index(struct reftable_writer *w)
 	w->index_cap = 0;
 }
 
-static const int debug = 0;
-
 static int writer_flush_nonempty_block(struct reftable_writer *w)
 {
+	struct reftable_index_record index_record = {
+		.last_key = STRBUF_INIT,
+	};
 	uint8_t typ = block_writer_type(w->block_writer);
-	struct reftable_block_stats *bstats =
-		writer_reftable_block_stats(w, typ);
-	uint64_t block_typ_off = (bstats->blocks == 0) ? w->next : 0;
-	int raw_bytes = block_writer_finish(w->block_writer);
-	int padding = 0;
-	int err = 0;
-	struct reftable_index_record ir = { .last_key = STRBUF_INIT };
+	struct reftable_block_stats *bstats;
+	int raw_bytes, padding = 0, err;
+	uint64_t block_typ_off;
+
+	/*
+	 * Finish the current block. This will cause the block writer to emit
+	 * restart points and potentially compress records in case we are
+	 * writing a log block.
+	 *
+	 * Note that this is still happening in memory.
+	 */
+	raw_bytes = block_writer_finish(w->block_writer);
 	if (raw_bytes < 0)
 		return raw_bytes;
 
-	if (!w->opts.unpadded && typ != BLOCK_TYPE_LOG) {
+	/*
+	 * By default, all records except for log records are padded to the
+	 * block size.
+	 */
+	if (!w->opts.unpadded && typ != BLOCK_TYPE_LOG)
 		padding = w->opts.block_size - raw_bytes;
-	}
 
-	if (block_typ_off > 0) {
+	bstats = writer_reftable_block_stats(w, typ);
+	block_typ_off = (bstats->blocks == 0) ? w->next : 0;
+	if (block_typ_off > 0)
 		bstats->offset = block_typ_off;
-	}
-
 	bstats->entries += w->block_writer->entries;
 	bstats->restarts += w->block_writer->restart_len;
 	bstats->blocks++;
 	w->stats.blocks++;
 
-	if (debug) {
-		fprintf(stderr, "block %c off %" PRIu64 " sz %d (%d)\n", typ,
-			w->next, raw_bytes,
-			get_be24(w->block + w->block_writer->header_off + 1));
-	}
-
-	if (w->next == 0) {
+	/*
+	 * If this is the first block we're writing to the table then we need
+	 * to also write the reftable header.
+	 */
+	if (!w->next)
 		writer_write_header(w, w->block);
-	}
 
 	err = padded_write(w, w->block, raw_bytes, padding);
 	if (err < 0)
 		return err;
 
+	/*
+	 * Add an index record for every block that we're writing. If we end up
+	 * having more than a threshold of index records we will end up writing
+	 * an index section in `writer_finish_section()`. Each index record
+	 * contains the last record key of the block it is indexing as well as
+	 * the offset of that block.
+	 *
+	 * Note that this also applies when flushing index blocks, in which
+	 * case we will end up with a multi-level index.
+	 */
 	REFTABLE_ALLOC_GROW(w->index, w->index_len + 1, w->index_cap);
-
-	ir.offset = w->next;
-	strbuf_reset(&ir.last_key);
-	strbuf_addbuf(&ir.last_key, &w->block_writer->last_key);
-	w->index[w->index_len] = ir;
-
+	index_record.offset = w->next;
+	strbuf_reset(&index_record.last_key);
+	strbuf_addbuf(&index_record.last_key, &w->block_writer->last_key);
+	w->index[w->index_len] = index_record;
 	w->index_len++;
+
 	w->next += padding + raw_bytes;
 	w->block_writer = NULL;
+
 	return 0;
 }
 
-- 
2.44.GIT


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[PATCH v2 08/11] reftable/writer: unify releasing memory

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 2139 bytes --]

There are two code paths which release memory of the reftable writer:

  - `reftable_writer_close()` releases internal state after it has
    written data.

  - `reftable_writer_free()` releases the block that was written to and
    the writer itself.

Both code paths free different parts of the writer, and consequently the
caller must make sure to call both. And while callers mostly do this
already, this falls apart when a write failure causes the caller to skip
calling `reftable_write_close()`.

Introduce a new function `reftable_writer_release()` that releases all
internal state and call it from both paths. Like this it is fine for the
caller to not call `reftable_writer_close()`.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 reftable/writer.c | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/reftable/writer.c b/reftable/writer.c
index d347ec4cc6..7b70c9b666 100644
--- a/reftable/writer.c
+++ b/reftable/writer.c
@@ -149,11 +149,21 @@ void reftable_writer_set_limits(struct reftable_writer *w, uint64_t min,
 	w->max_update_index = max;
 }
 
+static void reftable_writer_release(struct reftable_writer *w)
+{
+	if (w) {
+		reftable_free(w->block);
+		w->block = NULL;
+		block_writer_release(&w->block_writer_data);
+		w->block_writer = NULL;
+		writer_clear_index(w);
+		strbuf_release(&w->last_key);
+	}
+}
+
 void reftable_writer_free(struct reftable_writer *w)
 {
-	if (!w)
-		return;
-	reftable_free(w->block);
+	reftable_writer_release(w);
 	reftable_free(w);
 }
 
@@ -643,16 +653,13 @@ int reftable_writer_close(struct reftable_writer *w)
 	}
 
 done:
-	/* free up memory. */
-	block_writer_release(&w->block_writer_data);
-	writer_clear_index(w);
-	strbuf_release(&w->last_key);
+	reftable_writer_release(w);
 	return err;
 }
 
 static void writer_clear_index(struct reftable_writer *w)
 {
-	for (size_t i = 0; i < w->index_len; i++)
+	for (size_t i = 0; w->index && i < w->index_len; i++)
 		strbuf_release(&w->index[i].last_key);
 	FREE_AND_NULL(w->index);
 	w->index_len = 0;
-- 
2.44.GIT


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Re: [PATCH v2 08/11] reftable/writer: unify releasing memory

[Han-Wen Nienhuys]

On Thu, Apr 4, 2024 at 7:48 AM Patrick Steinhardt <ps@pks.im> wrote:
> There are two code paths which release memory of the reftable writer:
>
>   - `reftable_writer_close()` releases internal state after it has
>     written data.
>
>   - `reftable_writer_free()` releases the block that was written to and
>     the writer itself.

The bifurcation is there so you can read the stats after closing the
writer. The new method makes it harder to misuse, but now you have two
ways to end a writer. Suggestion: drop reftable_writer_{free,close}
from reftable-writer.h (rename to remove the reftable_ prefix because
they are no longer considered public) and find another way to read out
the stats. Either pass an optional reftable_writer_stats into the
construction of the writer, return the stats from the close function,
or drop stats altogether.  IIRC They are only used in the unit tests.

-- 
Han-Wen Nienhuys - hanwenn@gmail.com - http://www.xs4all.nl/~hanwen

Re: [PATCH v2 08/11] reftable/writer: unify releasing memory

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 1503 bytes --]

On Thu, Apr 04, 2024 at 09:08:46AM +0200, Han-Wen Nienhuys wrote:
> On Thu, Apr 4, 2024 at 7:48 AM Patrick Steinhardt <ps@pks.im> wrote:
> > There are two code paths which release memory of the reftable writer:
> >
> >   - `reftable_writer_close()` releases internal state after it has
> >     written data.
> >
> >   - `reftable_writer_free()` releases the block that was written to and
> >     the writer itself.
> 
> The bifurcation is there so you can read the stats after closing the
> writer. The new method makes it harder to misuse, but now you have two
> ways to end a writer. Suggestion: drop reftable_writer_{free,close}
> from reftable-writer.h (rename to remove the reftable_ prefix because
> they are no longer considered public) and find another way to read out
> the stats. Either pass an optional reftable_writer_stats into the
> construction of the writer, return the stats from the close function,
> or drop stats altogether.  IIRC They are only used in the unit tests.

But even with these refactorings the stats remain intact after calling
`reftable_writer_close()` or `reftable_writer_release()`, right? So it
basically continues to work as expected.

It might not be the cleanest way to handle this, but I think this patch
is an improvement over the previous state because we plug a memory leak
and deduplicate the cleanup logic. So I would suggest to defer your
proposed refactorings to a later point, if you're okay with that.

Thanks!

Patrick

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Re: [PATCH v2 08/11] reftable/writer: unify releasing memory

[Han-Wen Nienhuys]

On Thu, Apr 4, 2024 at 9:32 AM Patrick Steinhardt <ps@pks.im> wrote:
>
> On Thu, Apr 04, 2024 at 09:08:46AM +0200, Han-Wen Nienhuys wrote:
> > On Thu, Apr 4, 2024 at 7:48 AM Patrick Steinhardt <ps@pks.im> wrote:
> > > There are two code paths which release memory of the reftable writer:
> > >
> > >   - `reftable_writer_close()` releases internal state after it has
> > >     written data.
> > >
> > >   - `reftable_writer_free()` releases the block that was written to and
> > >     the writer itself.
> >
> > The bifurcation is there so you can read the stats after closing the
> > writer. The new method makes it harder to misuse, but now you have two
> > ways to end a writer. Suggestion: drop reftable_writer_{free,close}
> > from reftable-writer.h (rename to remove the reftable_ prefix because
> > they are no longer considered public) and find another way to read out
> > the stats. Either pass an optional reftable_writer_stats into the
> > construction of the writer, return the stats from the close function,
> > or drop stats altogether.  IIRC They are only used in the unit tests.
>
> But even with these refactorings the stats remain intact after calling
> `reftable_writer_close()` or `reftable_writer_release()`, right? So it
> basically continues to work as expected.

Right - I misinterpreted your change.

> It might not be the cleanest way to handle this, but I think this patch
> is an improvement over the previous state because we plug a memory leak
> and deduplicate the cleanup logic. So I would suggest to defer your
> proposed refactorings to a later point, if you're okay with that.

yes. Please add reftable_writer_release to reftable-writer.h for
consistency, though. Or remove the reftable_ prefix.

-- 
Han-Wen Nienhuys - hanwenn@gmail.com - http://www.xs4all.nl/~hanwen

Re: [PATCH v2 08/11] reftable/writer: unify releasing memory

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 775 bytes --]

On Thu, Apr 04, 2024 at 11:00:46AM +0200, Han-Wen Nienhuys wrote:
> On Thu, Apr 4, 2024 at 9:32 AM Patrick Steinhardt <ps@pks.im> wrote:
> > On Thu, Apr 04, 2024 at 09:08:46AM +0200, Han-Wen Nienhuys wrote:
[snip]
> > It might not be the cleanest way to handle this, but I think this patch
> > is an improvement over the previous state because we plug a memory leak
> > and deduplicate the cleanup logic. So I would suggest to defer your
> > proposed refactorings to a later point, if you're okay with that.
> 
> yes. Please add reftable_writer_release to reftable-writer.h for
> consistency, though. Or remove the reftable_ prefix.

I've dropped the `reftable_` prefix locally. Will wait a bit for
additional reviews though before sending out v3.

Patrick

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[PATCH v2 09/11] reftable/writer: reset `last_key` instead of releasing it

[Patrick Steinhardt]

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The reftable writer tracks the last key that it has written so that it
can properly compute the compressed prefix for the next record it is
about to write. This last key must be reset whenever we move on to write
the next block, which is done in `writer_reinit_block_writer()`. We do
this by calling `strbuf_release()` though, which needlessly deallocates
the underlying buffer.

Convert the code to use `strbuf_reset()` instead, which saves one
allocation per block we're about to write. This requires us to also
amend `reftable_writer_free()` to release the buffer's memory now as we
previously seemingly relied on `writer_reinit_block_writer()` to release
the memory for us. Releasing memory here is the right thing to do
anyway.

While at it, convert a callsite where we truncate the buffer by setting
its length to zero to instead use `strbuf_reset()`, too.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 reftable/writer.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/reftable/writer.c b/reftable/writer.c
index 7b70c9b666..32438e49b4 100644
--- a/reftable/writer.c
+++ b/reftable/writer.c
@@ -109,7 +109,7 @@ static void writer_reinit_block_writer(struct reftable_writer *w, uint8_t typ)
 		block_start = header_size(writer_version(w));
 	}
 
-	strbuf_release(&w->last_key);
+	strbuf_reset(&w->last_key);
 	block_writer_init(&w->block_writer_data, typ, w->block,
 			  w->opts.block_size, block_start,
 			  hash_size(w->opts.hash_id));
@@ -478,7 +478,7 @@ static int writer_finish_section(struct reftable_writer *w)
 	bstats->max_index_level = max_level;
 
 	/* Reinit lastKey, as the next section can start with any key. */
-	w->last_key.len = 0;
+	strbuf_reset(&w->last_key);
 
 	return 0;
 }
-- 
2.44.GIT


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[PATCH v2 10/11] reftable/block: reuse zstream when writing log blocks

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 5150 bytes --]

While most reftable blocks are written to disk as-is, blocks for log
records are compressed with zlib. To compress them we use `compress2()`,
which is a simple wrapper around the more complex `zstream` interface
that would require multiple function invocations.

One downside of this interface is that `compress2()` will reallocate
internal state of the `zstream` interface on every single invocation.
Consequently, as we call `compress2()` for every single log block which
we are about to write, this can lead to quite some memory allocation
churn.

Refactor the code so that the block writer reuses a `zstream`. This
significantly reduces the number of bytes allocated when writing many
refs in a single transaction, as demonstrated by the following benchmark
that writes 100k refs in a single transaction.

Before:

  HEAP SUMMARY:
      in use at exit: 671,931 bytes in 151 blocks
    total heap usage: 22,631,887 allocs, 22,631,736 frees, 1,854,670,793 bytes allocated

After:

  HEAP SUMMARY:
      in use at exit: 671,931 bytes in 151 blocks
    total heap usage: 22,620,528 allocs, 22,620,377 frees, 1,245,549,984 bytes allocated

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 reftable/block.c | 80 +++++++++++++++++++++++++++++++-----------------
 reftable/block.h |  1 +
 2 files changed, 53 insertions(+), 28 deletions(-)

diff --git a/reftable/block.c b/reftable/block.c
index e2a2cee58d..9129305515 100644
--- a/reftable/block.c
+++ b/reftable/block.c
@@ -76,6 +76,10 @@ void block_writer_init(struct block_writer *bw, uint8_t typ, uint8_t *buf,
 	bw->entries = 0;
 	bw->restart_len = 0;
 	bw->last_key.len = 0;
+	if (!bw->zstream) {
+		REFTABLE_CALLOC_ARRAY(bw->zstream, 1);
+		deflateInit(bw->zstream, 9);
+	}
 }
 
 uint8_t block_writer_type(struct block_writer *bw)
@@ -139,39 +143,57 @@ int block_writer_finish(struct block_writer *w)
 	w->next += 2;
 	put_be24(w->buf + 1 + w->header_off, w->next);
 
+	/*
+	 * Log records are stored zlib-compressed. Note that the compression
+	 * also spans over the restart points we have just written.
+	 */
 	if (block_writer_type(w) == BLOCK_TYPE_LOG) {
 		int block_header_skip = 4 + w->header_off;
-		uLongf src_len = w->next - block_header_skip;
-		uLongf dest_cap = src_len * 1.001 + 12;
-		uint8_t *compressed;
-
-		REFTABLE_ALLOC_ARRAY(compressed, dest_cap);
-
-		while (1) {
-			uLongf out_dest_len = dest_cap;
-			int zresult = compress2(compressed, &out_dest_len,
-						w->buf + block_header_skip,
-						src_len, 9);
-			if (zresult == Z_BUF_ERROR && dest_cap < LONG_MAX) {
-				dest_cap *= 2;
-				compressed =
-					reftable_realloc(compressed, dest_cap);
-				if (compressed)
-					continue;
-			}
-
-			if (Z_OK != zresult) {
-				reftable_free(compressed);
-				return REFTABLE_ZLIB_ERROR;
-			}
-
-			memcpy(w->buf + block_header_skip, compressed,
-			       out_dest_len);
-			w->next = out_dest_len + block_header_skip;
+		uLongf src_len = w->next - block_header_skip, compressed_len;
+		unsigned char *compressed;
+		int ret;
+
+		ret = deflateReset(w->zstream);
+		if (ret != Z_OK)
+			return REFTABLE_ZLIB_ERROR;
+
+		/*
+		 * Precompute the upper bound of how many bytes the compressed
+		 * data may end up with. Combined with `Z_FINISH`, `deflate()`
+		 * is guaranteed to return `Z_STREAM_END`.
+		 */
+		compressed_len = deflateBound(w->zstream, src_len);
+		REFTABLE_ALLOC_ARRAY(compressed, compressed_len);
+
+		w->zstream->next_out = compressed;
+		w->zstream->avail_out = compressed_len;
+		w->zstream->next_in = w->buf + block_header_skip;
+		w->zstream->avail_in = src_len;
+
+		/*
+		 * We want to perform all decompression in a single step, which
+		 * is why we can pass Z_FINISH here. As we have precomputed the
+		 * deflated buffer's size via `deflateBound()` this function is
+		 * guaranteed to succeed according to the zlib documentation.
+		 */
+		ret = deflate(w->zstream, Z_FINISH);
+		if (ret != Z_STREAM_END) {
 			reftable_free(compressed);
-			break;
+			return REFTABLE_ZLIB_ERROR;
 		}
+
+		/*
+		 * Overwrite the uncompressed data we have already written and
+		 * adjust the `next` pointer to point right after the
+		 * compressed data.
+		 */
+		memcpy(w->buf + block_header_skip, compressed,
+		       w->zstream->total_out);
+		w->next = w->zstream->total_out + block_header_skip;
+
+		reftable_free(compressed);
 	}
+
 	return w->next;
 }
 
@@ -425,6 +447,8 @@ int block_reader_seek(struct block_reader *br, struct block_iter *it,
 
 void block_writer_release(struct block_writer *bw)
 {
+	deflateEnd(bw->zstream);
+	FREE_AND_NULL(bw->zstream);
 	FREE_AND_NULL(bw->restarts);
 	strbuf_release(&bw->last_key);
 	/* the block is not owned. */
diff --git a/reftable/block.h b/reftable/block.h
index 47acc62c0a..1375957fc8 100644
--- a/reftable/block.h
+++ b/reftable/block.h
@@ -18,6 +18,7 @@ license that can be found in the LICENSE file or at
  * allocation overhead.
  */
 struct block_writer {
+	z_stream *zstream;
 	uint8_t *buf;
 	uint32_t block_size;
 
-- 
2.44.GIT


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[PATCH v2 11/11] reftable/block: reuse compressed array

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 3219 bytes --]

Similar to the preceding commit, let's reuse the `compressed` array that
we use to store compressed data in. This results in a small reduction in
memory allocations when writing many refs.

Before:

  HEAP SUMMARY:
      in use at exit: 671,931 bytes in 151 blocks
    total heap usage: 22,620,528 allocs, 22,620,377 frees, 1,245,549,984 bytes allocated

After:

  HEAP SUMMARY:
      in use at exit: 671,931 bytes in 151 blocks
    total heap usage: 22,618,257 allocs, 22,618,106 frees, 1,236,351,528 bytes allocated

So while the reduction in allocations isn't really all that big, it's a
low hanging fruit and thus there isn't much of a reason not to pick it.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 reftable/block.c | 14 +++++---------
 reftable/block.h |  3 +++
 2 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/reftable/block.c b/reftable/block.c
index 9129305515..f190c05520 100644
--- a/reftable/block.c
+++ b/reftable/block.c
@@ -150,7 +150,6 @@ int block_writer_finish(struct block_writer *w)
 	if (block_writer_type(w) == BLOCK_TYPE_LOG) {
 		int block_header_skip = 4 + w->header_off;
 		uLongf src_len = w->next - block_header_skip, compressed_len;
-		unsigned char *compressed;
 		int ret;
 
 		ret = deflateReset(w->zstream);
@@ -163,9 +162,9 @@ int block_writer_finish(struct block_writer *w)
 		 * is guaranteed to return `Z_STREAM_END`.
 		 */
 		compressed_len = deflateBound(w->zstream, src_len);
-		REFTABLE_ALLOC_ARRAY(compressed, compressed_len);
+		REFTABLE_ALLOC_GROW(w->compressed, compressed_len, w->compressed_cap);
 
-		w->zstream->next_out = compressed;
+		w->zstream->next_out = w->compressed;
 		w->zstream->avail_out = compressed_len;
 		w->zstream->next_in = w->buf + block_header_skip;
 		w->zstream->avail_in = src_len;
@@ -177,21 +176,17 @@ int block_writer_finish(struct block_writer *w)
 		 * guaranteed to succeed according to the zlib documentation.
 		 */
 		ret = deflate(w->zstream, Z_FINISH);
-		if (ret != Z_STREAM_END) {
-			reftable_free(compressed);
+		if (ret != Z_STREAM_END)
 			return REFTABLE_ZLIB_ERROR;
-		}
 
 		/*
 		 * Overwrite the uncompressed data we have already written and
 		 * adjust the `next` pointer to point right after the
 		 * compressed data.
 		 */
-		memcpy(w->buf + block_header_skip, compressed,
+		memcpy(w->buf + block_header_skip, w->compressed,
 		       w->zstream->total_out);
 		w->next = w->zstream->total_out + block_header_skip;
-
-		reftable_free(compressed);
 	}
 
 	return w->next;
@@ -450,6 +445,7 @@ void block_writer_release(struct block_writer *bw)
 	deflateEnd(bw->zstream);
 	FREE_AND_NULL(bw->zstream);
 	FREE_AND_NULL(bw->restarts);
+	FREE_AND_NULL(bw->compressed);
 	strbuf_release(&bw->last_key);
 	/* the block is not owned. */
 }
diff --git a/reftable/block.h b/reftable/block.h
index 1375957fc8..657498014c 100644
--- a/reftable/block.h
+++ b/reftable/block.h
@@ -19,6 +19,9 @@ license that can be found in the LICENSE file or at
  */
 struct block_writer {
 	z_stream *zstream;
+	unsigned char *compressed;
+	size_t compressed_cap;
+
 	uint8_t *buf;
 	uint32_t block_size;
 
-- 
2.44.GIT


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Re: [PATCH v2 00/11] reftable: optimize write performance

[Han-Wen Nienhuys]

On Thu, Apr 4, 2024 at 7:48 AM Patrick Steinhardt <ps@pks.im> wrote:
>
> Hi,
>
> this is the second version of my patch series that aims to optimize
> write performance in the reftable backend. I've made the following
> changes compared to v2:

Looks OK overall; I had a cursory glance.


-- 
Han-Wen Nienhuys - hanwenn@gmail.com - http://www.xs4all.nl/~hanwen

Re: [PATCH v2 00/11] reftable: optimize write performance

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 405 bytes --]

On Thu, Apr 04, 2024 at 09:09:53AM +0200, Han-Wen Nienhuys wrote:
> On Thu, Apr 4, 2024 at 7:48 AM Patrick Steinhardt <ps@pks.im> wrote:
> >
> > Hi,
> >
> > this is the second version of my patch series that aims to optimize
> > write performance in the reftable backend. I've made the following
> > changes compared to v2:
> 
> Looks OK overall; I had a cursory glance.

Thanks!

Patrick

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[PATCH v3 00/11] reftable: optimize write performance

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 7260 bytes --]

Hi,

this is the first version of my patch series that aims to optimize write
performance with the reftable backend.

Changes compared to v2:

    - The series now deepends on ps/reftable-binsearch-update at
      d51d8cc368 (reftable/block: avoid decoding keys when searching
      restart points, 2024-04-03). This is to resolve a merge conflict
      with that other series which has landed in "next" already.

    - Dropped the "reftable_" prefix from newly introduced internal
      reftable functions.

Thanks!

Patrick

Patrick Steinhardt (11):
  refs/reftable: fix D/F conflict error message on ref copy
  refs/reftable: perform explicit D/F check when writing symrefs
  refs/reftable: skip duplicate name checks
  reftable: remove name checks
  refs/reftable: don't recompute committer ident
  reftable/writer: refactorings for `writer_add_record()`
  reftable/writer: refactorings for `writer_flush_nonempty_block()`
  reftable/writer: unify releasing memory
  reftable/writer: reset `last_key` instead of releasing it
  reftable/block: reuse zstream when writing log blocks
  reftable/block: reuse compressed array

 Makefile                   |   2 -
 refs/reftable-backend.c    |  75 ++++++++++----
 reftable/block.c           |  80 ++++++++------
 reftable/block.h           |   4 +
 reftable/error.c           |   2 -
 reftable/refname.c         | 206 -------------------------------------
 reftable/refname.h         |  29 ------
 reftable/refname_test.c    | 101 ------------------
 reftable/reftable-error.h  |   3 -
 reftable/reftable-tests.h  |   1 -
 reftable/reftable-writer.h |   4 -
 reftable/stack.c           |  67 +-----------
 reftable/stack_test.c      |  39 -------
 reftable/writer.c          | 137 +++++++++++++++---------
 t/helper/test-reftable.c   |   1 -
 t/t0610-reftable-basics.sh |  35 ++++++-
 16 files changed, 230 insertions(+), 556 deletions(-)
 delete mode 100644 reftable/refname.c
 delete mode 100644 reftable/refname.h
 delete mode 100644 reftable/refname_test.c

Range-diff against v2:
 1:  926e802395 =  1:  bb735c389a refs/reftable: fix D/F conflict error message on ref copy
 2:  6190171906 =  2:  fe3f00d85a refs/reftable: perform explicit D/F check when writing symrefs
 3:  80008cc5e7 =  3:  763c6fdfcd refs/reftable: skip duplicate name checks
 4:  3497a570b4 !  4:  2a5f07627a reftable: remove name checks
    @@ reftable/refname.c (deleted)
     -#include "refname.h"
     -#include "reftable-iterator.h"
     -
    --struct find_arg {
    --	char **names;
    --	const char *want;
    +-struct refname_needle_lesseq_args {
    +-	char **haystack;
    +-	const char *needle;
     -};
     -
    --static int find_name(size_t k, void *arg)
    +-static int refname_needle_lesseq(size_t k, void *_args)
     -{
    --	struct find_arg *f_arg = arg;
    --	return strcmp(f_arg->names[k], f_arg->want) >= 0;
    +-	struct refname_needle_lesseq_args *args = _args;
    +-	return strcmp(args->needle, args->haystack[k]) <= 0;
     -}
     -
     -static int modification_has_ref(struct modification *mod, const char *name)
    @@ reftable/refname.c (deleted)
     -	int err = 0;
     -
     -	if (mod->add_len > 0) {
    --		struct find_arg arg = {
    --			.names = mod->add,
    --			.want = name,
    +-		struct refname_needle_lesseq_args args = {
    +-			.haystack = mod->add,
    +-			.needle = name,
     -		};
    --		int idx = binsearch(mod->add_len, find_name, &arg);
    --		if (idx < mod->add_len && !strcmp(mod->add[idx], name)) {
    +-		size_t idx = binsearch(mod->add_len, refname_needle_lesseq, &args);
    +-		if (idx < mod->add_len && !strcmp(mod->add[idx], name))
     -			return 0;
    --		}
     -	}
     -
     -	if (mod->del_len > 0) {
    --		struct find_arg arg = {
    --			.names = mod->del,
    --			.want = name,
    +-		struct refname_needle_lesseq_args args = {
    +-			.haystack = mod->del,
    +-			.needle = name,
     -		};
    --		int idx = binsearch(mod->del_len, find_name, &arg);
    --		if (idx < mod->del_len && !strcmp(mod->del[idx], name)) {
    +-		size_t idx = binsearch(mod->del_len, refname_needle_lesseq, &args);
    +-		if (idx < mod->del_len && !strcmp(mod->del[idx], name))
     -			return 1;
    --		}
     -	}
     -
     -	err = reftable_table_read_ref(&mod->tab, name, &ref);
    @@ reftable/refname.c (deleted)
     -	int err = 0;
     -
     -	if (mod->add_len > 0) {
    --		struct find_arg arg = {
    --			.names = mod->add,
    --			.want = prefix,
    +-		struct refname_needle_lesseq_args args = {
    +-			.haystack = mod->add,
    +-			.needle = prefix,
     -		};
    --		int idx = binsearch(mod->add_len, find_name, &arg);
    +-		size_t idx = binsearch(mod->add_len, refname_needle_lesseq, &args);
     -		if (idx < mod->add_len &&
     -		    !strncmp(prefix, mod->add[idx], strlen(prefix)))
     -			goto done;
    @@ reftable/refname.c (deleted)
     -			goto done;
     -
     -		if (mod->del_len > 0) {
    --			struct find_arg arg = {
    --				.names = mod->del,
    --				.want = ref.refname,
    +-			struct refname_needle_lesseq_args args = {
    +-				.haystack = mod->del,
    +-				.needle = ref.refname,
     -			};
    --			int idx = binsearch(mod->del_len, find_name, &arg);
    +-			size_t idx = binsearch(mod->del_len, refname_needle_lesseq, &args);
     -			if (idx < mod->del_len &&
    --			    !strcmp(ref.refname, mod->del[idx])) {
    +-			    !strcmp(ref.refname, mod->del[idx]))
     -				continue;
    --			}
     -		}
     -
     -		if (strncmp(ref.refname, prefix, strlen(prefix))) {
 5:  f892a3007b =  5:  1ca7d9b6cf refs/reftable: don't recompute committer ident
 6:  4877ab3921 =  6:  deabf82186 reftable/writer: refactorings for `writer_add_record()`
 7:  8f1c5b4169 =  7:  d47ad49d49 reftable/writer: refactorings for `writer_flush_nonempty_block()`
 8:  41db7414e1 !  8:  76d4a1f73b reftable/writer: unify releasing memory
    @@ reftable/writer.c: void reftable_writer_set_limits(struct reftable_writer *w, ui
      	w->max_update_index = max;
      }
      
    -+static void reftable_writer_release(struct reftable_writer *w)
    ++static void writer_release(struct reftable_writer *w)
     +{
     +	if (w) {
     +		reftable_free(w->block);
    @@ reftable/writer.c: void reftable_writer_set_limits(struct reftable_writer *w, ui
     -	if (!w)
     -		return;
     -	reftable_free(w->block);
    -+	reftable_writer_release(w);
    ++	writer_release(w);
      	reftable_free(w);
      }
      
    @@ reftable/writer.c: int reftable_writer_close(struct reftable_writer *w)
     -	block_writer_release(&w->block_writer_data);
     -	writer_clear_index(w);
     -	strbuf_release(&w->last_key);
    -+	reftable_writer_release(w);
    ++	writer_release(w);
      	return err;
      }
      
 9:  e5c7dbe417 =  9:  722ab0ee28 reftable/writer: reset `last_key` instead of releasing it
10:  26f422703f = 10:  962a96003b reftable/block: reuse zstream when writing log blocks
11:  4f9df714da = 11:  323892841a reftable/block: reuse compressed array

base-commit: 7774cfed6261ce2900c84e55906da708c711d601
-- 
2.44.GIT


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[PATCH v3 01/11] refs/reftable: fix D/F conflict error message on ref copy

[Patrick Steinhardt]

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The `write_copy_table()` function is shared between the reftable
implementations for renaming and copying refs. The only difference
between those two cases is that the rename will also delete the old
reference, whereas copying won't.

This has resulted in a bug though where we don't properly verify refname
availability. When calling `refs_verify_refname_available()`, we always
add the old ref name to the list of refs to be skipped when computing
availability, which indicates that the name would be available even if
it already exists at the current point in time. This is only the right
thing to do for renames though, not for copies.

The consequence of this bug is quite harmless because the reftable
backend has its own checks for D/F conflicts further down in the call
stack, and thus we refuse the update regardless of the bug. But all the
user gets in this case is an uninformative message that copying the ref
has failed, without any further details.

Fix the bug and only add the old name to the skip-list in case we rename
the ref. Consequently, this error case will now be handled by
`refs_verify_refname_available()`, which knows to provide a proper error
message.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 refs/reftable-backend.c    |  3 ++-
 t/t0610-reftable-basics.sh | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index e206d5a073..0358da14db 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -1351,7 +1351,8 @@ static int write_copy_table(struct reftable_writer *writer, void *cb_data)
 	/*
 	 * Verify that the new refname is available.
 	 */
-	string_list_insert(&skip, arg->oldname);
+	if (arg->delete_old)
+		string_list_insert(&skip, arg->oldname);
 	ret = refs_verify_refname_available(&arg->refs->base, arg->newname,
 					    NULL, &skip, &errbuf);
 	if (ret < 0) {
diff --git a/t/t0610-reftable-basics.sh b/t/t0610-reftable-basics.sh
index 686781192e..055231a707 100755
--- a/t/t0610-reftable-basics.sh
+++ b/t/t0610-reftable-basics.sh
@@ -730,6 +730,39 @@ test_expect_success 'reflog: updates via HEAD update HEAD reflog' '
 	)
 '
 
+test_expect_success 'branch: copying branch with D/F conflict' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit A &&
+		git branch branch &&
+		cat >expect <<-EOF &&
+		error: ${SQ}refs/heads/branch${SQ} exists; cannot create ${SQ}refs/heads/branch/moved${SQ}
+		fatal: branch copy failed
+		EOF
+		test_must_fail git branch -c branch branch/moved 2>err &&
+		test_cmp expect err
+	)
+'
+
+test_expect_success 'branch: moving branch with D/F conflict' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit A &&
+		git branch branch &&
+		git branch conflict &&
+		cat >expect <<-EOF &&
+		error: ${SQ}refs/heads/conflict${SQ} exists; cannot create ${SQ}refs/heads/conflict/moved${SQ}
+		fatal: branch rename failed
+		EOF
+		test_must_fail git branch -m branch conflict/moved 2>err &&
+		test_cmp expect err
+	)
+'
+
 test_expect_success 'worktree: adding worktree creates separate stack' '
 	test_when_finished "rm -rf repo worktree" &&
 	git init repo &&
-- 
2.44.GIT


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[PATCH v3 02/11] refs/reftable: perform explicit D/F check when writing symrefs

[Patrick Steinhardt]

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We already perform explicit D/F checks in all reftable callbacks which
write refs, except when writing symrefs. For one this leads to an error
message which isn't perfectly actionable because we only tell the user
that there was a D/F conflict, but not which refs conflicted with each
other. But second, once all ref updating callbacks explicitly check for
D/F conflicts, we can disable the D/F checks in the reftable library
itself and thus avoid some duplicated efforts.

Refactor the code that writes symref tables to explicitly call into
`refs_verify_refname_available()` when writing symrefs.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 refs/reftable-backend.c    | 20 +++++++++++++++++---
 t/t0610-reftable-basics.sh |  2 +-
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 0358da14db..8a54b0d8b2 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -1217,6 +1217,7 @@ static int reftable_be_pack_refs(struct ref_store *ref_store,
 struct write_create_symref_arg {
 	struct reftable_ref_store *refs;
 	struct reftable_stack *stack;
+	struct strbuf *err;
 	const char *refname;
 	const char *target;
 	const char *logmsg;
@@ -1239,6 +1240,11 @@ static int write_create_symref_table(struct reftable_writer *writer, void *cb_da
 
 	reftable_writer_set_limits(writer, ts, ts);
 
+	ret = refs_verify_refname_available(&create->refs->base, create->refname,
+					    NULL, NULL, create->err);
+	if (ret < 0)
+		return ret;
+
 	ret = reftable_writer_add_ref(writer, &ref);
 	if (ret)
 		return ret;
@@ -1280,12 +1286,14 @@ static int reftable_be_create_symref(struct ref_store *ref_store,
 	struct reftable_ref_store *refs =
 		reftable_be_downcast(ref_store, REF_STORE_WRITE, "create_symref");
 	struct reftable_stack *stack = stack_for(refs, refname, &refname);
+	struct strbuf err = STRBUF_INIT;
 	struct write_create_symref_arg arg = {
 		.refs = refs,
 		.stack = stack,
 		.refname = refname,
 		.target = target,
 		.logmsg = logmsg,
+		.err = &err,
 	};
 	int ret;
 
@@ -1301,9 +1309,15 @@ static int reftable_be_create_symref(struct ref_store *ref_store,
 
 done:
 	assert(ret != REFTABLE_API_ERROR);
-	if (ret)
-		error("unable to write symref for %s: %s", refname,
-		      reftable_error_str(ret));
+	if (ret) {
+		if (err.len)
+			error("%s", err.buf);
+		else
+			error("unable to write symref for %s: %s", refname,
+			      reftable_error_str(ret));
+	}
+
+	strbuf_release(&err);
 	return ret;
 }
 
diff --git a/t/t0610-reftable-basics.sh b/t/t0610-reftable-basics.sh
index 055231a707..12b0004781 100755
--- a/t/t0610-reftable-basics.sh
+++ b/t/t0610-reftable-basics.sh
@@ -255,7 +255,7 @@ test_expect_success 'ref transaction: creating symbolic ref fails with F/D confl
 	git init repo &&
 	test_commit -C repo A &&
 	cat >expect <<-EOF &&
-	error: unable to write symref for refs/heads: file/directory conflict
+	error: ${SQ}refs/heads/main${SQ} exists; cannot create ${SQ}refs/heads${SQ}
 	EOF
 	test_must_fail git -C repo symbolic-ref refs/heads refs/heads/foo 2>err &&
 	test_cmp expect err
-- 
2.44.GIT


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[PATCH v3 03/11] refs/reftable: skip duplicate name checks

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 2249 bytes --]

All the callback functions which write refs in the reftable backend
perform D/F conflict checks via `refs_verify_refname_available()`. But
in reality we perform these D/F conflict checks a second time in the
reftable library via `stack_check_addition()`.

Interestingly, the code in the reftable library is inferior compared to
the generic function:

  - It is slower than `refs_verify_refname_available()`, even though
    this can probably be optimized.

  - It does not provide a proper error message to the caller, and thus
    all the user would see is a generic "file/directory conflict"
    message.

Disable the D/F conflict checks in the reftable library by setting the
`skip_name_check` write option. This results in a non-negligible speedup
when writing many refs. The following benchmark writes 100k refs in a
single transaction:

  Benchmark 1: update-ref: create many refs (HEAD~)
    Time (mean ± σ):      3.241 s ±  0.040 s    [User: 1.854 s, System: 1.381 s]
    Range (min … max):    3.185 s …  3.454 s    100 runs

  Benchmark 2: update-ref: create many refs (HEAD)
    Time (mean ± σ):      2.878 s ±  0.024 s    [User: 1.506 s, System: 1.367 s]
    Range (min … max):    2.838 s …  2.960 s    100 runs

  Summary
    update-ref: create many refs (HEAD~) ran
      1.13 ± 0.02 times faster than update-ref: create many refs (HEAD)

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 refs/reftable-backend.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 8a54b0d8b2..7515dd3019 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -247,6 +247,11 @@ static struct ref_store *reftable_be_init(struct repository *repo,
 	refs->write_options.block_size = 4096;
 	refs->write_options.hash_id = repo->hash_algo->format_id;
 	refs->write_options.default_permissions = calc_shared_perm(0666 & ~mask);
+	/*
+	 * We verify names via `refs_verify_refname_available()`, so there is
+	 * no need to do the same checks in the reftable library again.
+	 */
+	refs->write_options.skip_name_check = 1;
 
 	/*
 	 * Set up the main reftable stack that is hosted in GIT_COMMON_DIR.
-- 
2.44.GIT


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[PATCH v3 04/11] reftable: remove name checks

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 18516 bytes --]

In the preceding commit we have disabled name checks in the "reftable"
backend. These checks were responsible for verifying multiple things
when writing records to the reftable stack:

  - Detecting file/directory conflicts. Starting with the preceding
    commits this is now handled by the reftable backend itself via
    `refs_verify_refname_available()`.

  - Validating refnames. This is handled by `check_refname_format()` in
    the generic ref transacton layer.

The code in the reftable library is thus not used anymore and likely to
bitrot over time. Remove it.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 Makefile                   |   2 -
 refs/reftable-backend.c    |   5 -
 reftable/error.c           |   2 -
 reftable/refname.c         | 206 -------------------------------------
 reftable/refname.h         |  29 ------
 reftable/refname_test.c    | 101 ------------------
 reftable/reftable-error.h  |   3 -
 reftable/reftable-tests.h  |   1 -
 reftable/reftable-writer.h |   4 -
 reftable/stack.c           |  67 +-----------
 reftable/stack_test.c      |  39 -------
 t/helper/test-reftable.c   |   1 -
 12 files changed, 1 insertion(+), 459 deletions(-)
 delete mode 100644 reftable/refname.c
 delete mode 100644 reftable/refname.h
 delete mode 100644 reftable/refname_test.c

diff --git a/Makefile b/Makefile
index c43c1bd1a0..05e3d37581 100644
--- a/Makefile
+++ b/Makefile
@@ -2655,7 +2655,6 @@ REFTABLE_OBJS += reftable/merged.o
 REFTABLE_OBJS += reftable/pq.o
 REFTABLE_OBJS += reftable/reader.o
 REFTABLE_OBJS += reftable/record.o
-REFTABLE_OBJS += reftable/refname.o
 REFTABLE_OBJS += reftable/generic.o
 REFTABLE_OBJS += reftable/stack.o
 REFTABLE_OBJS += reftable/tree.o
@@ -2668,7 +2667,6 @@ REFTABLE_TEST_OBJS += reftable/merged_test.o
 REFTABLE_TEST_OBJS += reftable/pq_test.o
 REFTABLE_TEST_OBJS += reftable/record_test.o
 REFTABLE_TEST_OBJS += reftable/readwrite_test.o
-REFTABLE_TEST_OBJS += reftable/refname_test.o
 REFTABLE_TEST_OBJS += reftable/stack_test.o
 REFTABLE_TEST_OBJS += reftable/test_framework.o
 REFTABLE_TEST_OBJS += reftable/tree_test.o
diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 7515dd3019..8a54b0d8b2 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -247,11 +247,6 @@ static struct ref_store *reftable_be_init(struct repository *repo,
 	refs->write_options.block_size = 4096;
 	refs->write_options.hash_id = repo->hash_algo->format_id;
 	refs->write_options.default_permissions = calc_shared_perm(0666 & ~mask);
-	/*
-	 * We verify names via `refs_verify_refname_available()`, so there is
-	 * no need to do the same checks in the reftable library again.
-	 */
-	refs->write_options.skip_name_check = 1;
 
 	/*
 	 * Set up the main reftable stack that is hosted in GIT_COMMON_DIR.
diff --git a/reftable/error.c b/reftable/error.c
index 0d1766735e..169f89d2f1 100644
--- a/reftable/error.c
+++ b/reftable/error.c
@@ -27,8 +27,6 @@ const char *reftable_error_str(int err)
 		return "misuse of the reftable API";
 	case REFTABLE_ZLIB_ERROR:
 		return "zlib failure";
-	case REFTABLE_NAME_CONFLICT:
-		return "file/directory conflict";
 	case REFTABLE_EMPTY_TABLE_ERROR:
 		return "wrote empty table";
 	case REFTABLE_REFNAME_ERROR:
diff --git a/reftable/refname.c b/reftable/refname.c
deleted file mode 100644
index bbfde15754..0000000000
--- a/reftable/refname.c
+++ /dev/null
@@ -1,206 +0,0 @@
-/*
-  Copyright 2020 Google LLC
-
-  Use of this source code is governed by a BSD-style
-  license that can be found in the LICENSE file or at
-  https://developers.google.com/open-source/licenses/bsd
-*/
-
-#include "system.h"
-#include "reftable-error.h"
-#include "basics.h"
-#include "refname.h"
-#include "reftable-iterator.h"
-
-struct refname_needle_lesseq_args {
-	char **haystack;
-	const char *needle;
-};
-
-static int refname_needle_lesseq(size_t k, void *_args)
-{
-	struct refname_needle_lesseq_args *args = _args;
-	return strcmp(args->needle, args->haystack[k]) <= 0;
-}
-
-static int modification_has_ref(struct modification *mod, const char *name)
-{
-	struct reftable_ref_record ref = { NULL };
-	int err = 0;
-
-	if (mod->add_len > 0) {
-		struct refname_needle_lesseq_args args = {
-			.haystack = mod->add,
-			.needle = name,
-		};
-		size_t idx = binsearch(mod->add_len, refname_needle_lesseq, &args);
-		if (idx < mod->add_len && !strcmp(mod->add[idx], name))
-			return 0;
-	}
-
-	if (mod->del_len > 0) {
-		struct refname_needle_lesseq_args args = {
-			.haystack = mod->del,
-			.needle = name,
-		};
-		size_t idx = binsearch(mod->del_len, refname_needle_lesseq, &args);
-		if (idx < mod->del_len && !strcmp(mod->del[idx], name))
-			return 1;
-	}
-
-	err = reftable_table_read_ref(&mod->tab, name, &ref);
-	reftable_ref_record_release(&ref);
-	return err;
-}
-
-static void modification_release(struct modification *mod)
-{
-	/* don't delete the strings themselves; they're owned by ref records.
-	 */
-	FREE_AND_NULL(mod->add);
-	FREE_AND_NULL(mod->del);
-	mod->add_len = 0;
-	mod->del_len = 0;
-}
-
-static int modification_has_ref_with_prefix(struct modification *mod,
-					    const char *prefix)
-{
-	struct reftable_iterator it = { NULL };
-	struct reftable_ref_record ref = { NULL };
-	int err = 0;
-
-	if (mod->add_len > 0) {
-		struct refname_needle_lesseq_args args = {
-			.haystack = mod->add,
-			.needle = prefix,
-		};
-		size_t idx = binsearch(mod->add_len, refname_needle_lesseq, &args);
-		if (idx < mod->add_len &&
-		    !strncmp(prefix, mod->add[idx], strlen(prefix)))
-			goto done;
-	}
-	err = reftable_table_seek_ref(&mod->tab, &it, prefix);
-	if (err)
-		goto done;
-
-	while (1) {
-		err = reftable_iterator_next_ref(&it, &ref);
-		if (err)
-			goto done;
-
-		if (mod->del_len > 0) {
-			struct refname_needle_lesseq_args args = {
-				.haystack = mod->del,
-				.needle = ref.refname,
-			};
-			size_t idx = binsearch(mod->del_len, refname_needle_lesseq, &args);
-			if (idx < mod->del_len &&
-			    !strcmp(ref.refname, mod->del[idx]))
-				continue;
-		}
-
-		if (strncmp(ref.refname, prefix, strlen(prefix))) {
-			err = 1;
-			goto done;
-		}
-		err = 0;
-		goto done;
-	}
-
-done:
-	reftable_ref_record_release(&ref);
-	reftable_iterator_destroy(&it);
-	return err;
-}
-
-static int validate_refname(const char *name)
-{
-	while (1) {
-		char *next = strchr(name, '/');
-		if (!*name) {
-			return REFTABLE_REFNAME_ERROR;
-		}
-		if (!next) {
-			return 0;
-		}
-		if (next - name == 0 || (next - name == 1 && *name == '.') ||
-		    (next - name == 2 && name[0] == '.' && name[1] == '.'))
-			return REFTABLE_REFNAME_ERROR;
-		name = next + 1;
-	}
-	return 0;
-}
-
-int validate_ref_record_addition(struct reftable_table tab,
-				 struct reftable_ref_record *recs, size_t sz)
-{
-	struct modification mod = {
-		.tab = tab,
-		.add = reftable_calloc(sz, sizeof(*mod.add)),
-		.del = reftable_calloc(sz, sizeof(*mod.del)),
-	};
-	int i = 0;
-	int err = 0;
-	for (; i < sz; i++) {
-		if (reftable_ref_record_is_deletion(&recs[i])) {
-			mod.del[mod.del_len++] = recs[i].refname;
-		} else {
-			mod.add[mod.add_len++] = recs[i].refname;
-		}
-	}
-
-	err = modification_validate(&mod);
-	modification_release(&mod);
-	return err;
-}
-
-static void strbuf_trim_component(struct strbuf *sl)
-{
-	while (sl->len > 0) {
-		int is_slash = (sl->buf[sl->len - 1] == '/');
-		strbuf_setlen(sl, sl->len - 1);
-		if (is_slash)
-			break;
-	}
-}
-
-int modification_validate(struct modification *mod)
-{
-	struct strbuf slashed = STRBUF_INIT;
-	int err = 0;
-	int i = 0;
-	for (; i < mod->add_len; i++) {
-		err = validate_refname(mod->add[i]);
-		if (err)
-			goto done;
-		strbuf_reset(&slashed);
-		strbuf_addstr(&slashed, mod->add[i]);
-		strbuf_addstr(&slashed, "/");
-
-		err = modification_has_ref_with_prefix(mod, slashed.buf);
-		if (err == 0) {
-			err = REFTABLE_NAME_CONFLICT;
-			goto done;
-		}
-		if (err < 0)
-			goto done;
-
-		strbuf_reset(&slashed);
-		strbuf_addstr(&slashed, mod->add[i]);
-		while (slashed.len) {
-			strbuf_trim_component(&slashed);
-			err = modification_has_ref(mod, slashed.buf);
-			if (err == 0) {
-				err = REFTABLE_NAME_CONFLICT;
-				goto done;
-			}
-			if (err < 0)
-				goto done;
-		}
-	}
-	err = 0;
-done:
-	strbuf_release(&slashed);
-	return err;
-}
diff --git a/reftable/refname.h b/reftable/refname.h
deleted file mode 100644
index a24b40fcb4..0000000000
--- a/reftable/refname.h
+++ /dev/null
@@ -1,29 +0,0 @@
-/*
-  Copyright 2020 Google LLC
-
-  Use of this source code is governed by a BSD-style
-  license that can be found in the LICENSE file or at
-  https://developers.google.com/open-source/licenses/bsd
-*/
-#ifndef REFNAME_H
-#define REFNAME_H
-
-#include "reftable-record.h"
-#include "reftable-generic.h"
-
-struct modification {
-	struct reftable_table tab;
-
-	char **add;
-	size_t add_len;
-
-	char **del;
-	size_t del_len;
-};
-
-int validate_ref_record_addition(struct reftable_table tab,
-				 struct reftable_ref_record *recs, size_t sz);
-
-int modification_validate(struct modification *mod);
-
-#endif
diff --git a/reftable/refname_test.c b/reftable/refname_test.c
deleted file mode 100644
index b9cc62554e..0000000000
--- a/reftable/refname_test.c
+++ /dev/null
@@ -1,101 +0,0 @@
-/*
-Copyright 2020 Google LLC
-
-Use of this source code is governed by a BSD-style
-license that can be found in the LICENSE file or at
-https://developers.google.com/open-source/licenses/bsd
-*/
-
-#include "basics.h"
-#include "block.h"
-#include "blocksource.h"
-#include "reader.h"
-#include "record.h"
-#include "refname.h"
-#include "reftable-error.h"
-#include "reftable-writer.h"
-#include "system.h"
-
-#include "test_framework.h"
-#include "reftable-tests.h"
-
-struct testcase {
-	char *add;
-	char *del;
-	int error_code;
-};
-
-static void test_conflict(void)
-{
-	struct reftable_write_options opts = { 0 };
-	struct strbuf buf = STRBUF_INIT;
-	struct reftable_writer *w =
-		reftable_new_writer(&strbuf_add_void, &noop_flush, &buf, &opts);
-	struct reftable_ref_record rec = {
-		.refname = "a/b",
-		.value_type = REFTABLE_REF_SYMREF,
-		.value.symref = "destination", /* make sure it's not a symref.
-						*/
-		.update_index = 1,
-	};
-	int err;
-	int i;
-	struct reftable_block_source source = { NULL };
-	struct reftable_reader *rd = NULL;
-	struct reftable_table tab = { NULL };
-	struct testcase cases[] = {
-		{ "a/b/c", NULL, REFTABLE_NAME_CONFLICT },
-		{ "b", NULL, 0 },
-		{ "a", NULL, REFTABLE_NAME_CONFLICT },
-		{ "a", "a/b", 0 },
-
-		{ "p/", NULL, REFTABLE_REFNAME_ERROR },
-		{ "p//q", NULL, REFTABLE_REFNAME_ERROR },
-		{ "p/./q", NULL, REFTABLE_REFNAME_ERROR },
-		{ "p/../q", NULL, REFTABLE_REFNAME_ERROR },
-
-		{ "a/b/c", "a/b", 0 },
-		{ NULL, "a//b", 0 },
-	};
-	reftable_writer_set_limits(w, 1, 1);
-
-	err = reftable_writer_add_ref(w, &rec);
-	EXPECT_ERR(err);
-
-	err = reftable_writer_close(w);
-	EXPECT_ERR(err);
-	reftable_writer_free(w);
-
-	block_source_from_strbuf(&source, &buf);
-	err = reftable_new_reader(&rd, &source, "filename");
-	EXPECT_ERR(err);
-
-	reftable_table_from_reader(&tab, rd);
-
-	for (i = 0; i < ARRAY_SIZE(cases); i++) {
-		struct modification mod = {
-			.tab = tab,
-		};
-
-		if (cases[i].add) {
-			mod.add = &cases[i].add;
-			mod.add_len = 1;
-		}
-		if (cases[i].del) {
-			mod.del = &cases[i].del;
-			mod.del_len = 1;
-		}
-
-		err = modification_validate(&mod);
-		EXPECT(err == cases[i].error_code);
-	}
-
-	reftable_reader_free(rd);
-	strbuf_release(&buf);
-}
-
-int refname_test_main(int argc, const char *argv[])
-{
-	RUN_TEST(test_conflict);
-	return 0;
-}
diff --git a/reftable/reftable-error.h b/reftable/reftable-error.h
index 4c457aaaf8..3a5f5b92c6 100644
--- a/reftable/reftable-error.h
+++ b/reftable/reftable-error.h
@@ -48,9 +48,6 @@ enum reftable_error {
 	/* Wrote a table without blocks. */
 	REFTABLE_EMPTY_TABLE_ERROR = -8,
 
-	/* Dir/file conflict. */
-	REFTABLE_NAME_CONFLICT = -9,
-
 	/* Invalid ref name. */
 	REFTABLE_REFNAME_ERROR = -10,
 
diff --git a/reftable/reftable-tests.h b/reftable/reftable-tests.h
index 0019cbcfa4..114cc3d053 100644
--- a/reftable/reftable-tests.h
+++ b/reftable/reftable-tests.h
@@ -14,7 +14,6 @@ int block_test_main(int argc, const char **argv);
 int merged_test_main(int argc, const char **argv);
 int pq_test_main(int argc, const char **argv);
 int record_test_main(int argc, const char **argv);
-int refname_test_main(int argc, const char **argv);
 int readwrite_test_main(int argc, const char **argv);
 int stack_test_main(int argc, const char **argv);
 int tree_test_main(int argc, const char **argv);
diff --git a/reftable/reftable-writer.h b/reftable/reftable-writer.h
index 7c7cae5f99..3c119e2bbb 100644
--- a/reftable/reftable-writer.h
+++ b/reftable/reftable-writer.h
@@ -38,10 +38,6 @@ struct reftable_write_options {
 	/* Default mode for creating files. If unset, use 0666 (+umask) */
 	unsigned int default_permissions;
 
-	/* boolean: do not check ref names for validity or dir/file conflicts.
-	 */
-	unsigned skip_name_check : 1;
-
 	/* boolean: copy log messages exactly. If unset, check that the message
 	 *   is a single line, and add '\n' if missing.
 	 */
diff --git a/reftable/stack.c b/reftable/stack.c
index 1ecf1b9751..e264df5ced 100644
--- a/reftable/stack.c
+++ b/reftable/stack.c
@@ -12,8 +12,8 @@ license that can be found in the LICENSE file or at
 #include "system.h"
 #include "merged.h"
 #include "reader.h"
-#include "refname.h"
 #include "reftable-error.h"
+#include "reftable-generic.h"
 #include "reftable-record.h"
 #include "reftable-merged.h"
 #include "writer.h"
@@ -27,8 +27,6 @@ static int stack_write_compact(struct reftable_stack *st,
 			       struct reftable_writer *wr,
 			       size_t first, size_t last,
 			       struct reftable_log_expiry_config *config);
-static int stack_check_addition(struct reftable_stack *st,
-				const char *new_tab_name);
 static void reftable_addition_close(struct reftable_addition *add);
 static int reftable_stack_reload_maybe_reuse(struct reftable_stack *st,
 					     int reuse_open);
@@ -781,10 +779,6 @@ int reftable_addition_add(struct reftable_addition *add,
 		goto done;
 	}
 
-	err = stack_check_addition(add->stack, get_tempfile_path(tab_file));
-	if (err < 0)
-		goto done;
-
 	if (wr->min_update_index < add->next_update_index) {
 		err = REFTABLE_API_ERROR;
 		goto done;
@@ -1340,65 +1334,6 @@ int reftable_stack_read_log(struct reftable_stack *st, const char *refname,
 	return err;
 }
 
-static int stack_check_addition(struct reftable_stack *st,
-				const char *new_tab_name)
-{
-	int err = 0;
-	struct reftable_block_source src = { NULL };
-	struct reftable_reader *rd = NULL;
-	struct reftable_table tab = { NULL };
-	struct reftable_ref_record *refs = NULL;
-	struct reftable_iterator it = { NULL };
-	int cap = 0;
-	int len = 0;
-	int i = 0;
-
-	if (st->config.skip_name_check)
-		return 0;
-
-	err = reftable_block_source_from_file(&src, new_tab_name);
-	if (err < 0)
-		goto done;
-
-	err = reftable_new_reader(&rd, &src, new_tab_name);
-	if (err < 0)
-		goto done;
-
-	err = reftable_reader_seek_ref(rd, &it, "");
-	if (err > 0) {
-		err = 0;
-		goto done;
-	}
-	if (err < 0)
-		goto done;
-
-	while (1) {
-		struct reftable_ref_record ref = { NULL };
-		err = reftable_iterator_next_ref(&it, &ref);
-		if (err > 0)
-			break;
-		if (err < 0)
-			goto done;
-
-		REFTABLE_ALLOC_GROW(refs, len + 1, cap);
-		refs[len++] = ref;
-	}
-
-	reftable_table_from_merged_table(&tab, reftable_stack_merged_table(st));
-
-	err = validate_ref_record_addition(tab, refs, len);
-
-done:
-	for (i = 0; i < len; i++) {
-		reftable_ref_record_release(&refs[i]);
-	}
-
-	free(refs);
-	reftable_iterator_destroy(&it);
-	reftable_reader_free(rd);
-	return err;
-}
-
 static int is_table_name(const char *s)
 {
 	const char *dot = strrchr(s, '.');
diff --git a/reftable/stack_test.c b/reftable/stack_test.c
index 0dc9a44648..b88097c3b6 100644
--- a/reftable/stack_test.c
+++ b/reftable/stack_test.c
@@ -353,44 +353,6 @@ static void test_reftable_stack_transaction_api_performs_auto_compaction(void)
 	clear_dir(dir);
 }
 
-static void test_reftable_stack_validate_refname(void)
-{
-	struct reftable_write_options cfg = { 0 };
-	struct reftable_stack *st = NULL;
-	int err;
-	char *dir = get_tmp_dir(__LINE__);
-
-	int i;
-	struct reftable_ref_record ref = {
-		.refname = "a/b",
-		.update_index = 1,
-		.value_type = REFTABLE_REF_SYMREF,
-		.value.symref = "master",
-	};
-	char *additions[] = { "a", "a/b/c" };
-
-	err = reftable_new_stack(&st, dir, cfg);
-	EXPECT_ERR(err);
-
-	err = reftable_stack_add(st, &write_test_ref, &ref);
-	EXPECT_ERR(err);
-
-	for (i = 0; i < ARRAY_SIZE(additions); i++) {
-		struct reftable_ref_record ref = {
-			.refname = additions[i],
-			.update_index = 1,
-			.value_type = REFTABLE_REF_SYMREF,
-			.value.symref = "master",
-		};
-
-		err = reftable_stack_add(st, &write_test_ref, &ref);
-		EXPECT(err == REFTABLE_NAME_CONFLICT);
-	}
-
-	reftable_stack_destroy(st);
-	clear_dir(dir);
-}
-
 static int write_error(struct reftable_writer *wr, void *arg)
 {
 	return *((int *)arg);
@@ -1097,7 +1059,6 @@ int stack_test_main(int argc, const char *argv[])
 	RUN_TEST(test_reftable_stack_transaction_api_performs_auto_compaction);
 	RUN_TEST(test_reftable_stack_update_index_check);
 	RUN_TEST(test_reftable_stack_uptodate);
-	RUN_TEST(test_reftable_stack_validate_refname);
 	RUN_TEST(test_sizes_to_segments);
 	RUN_TEST(test_sizes_to_segments_all_equal);
 	RUN_TEST(test_sizes_to_segments_empty);
diff --git a/t/helper/test-reftable.c b/t/helper/test-reftable.c
index 00237ef0d9..bae731669c 100644
--- a/t/helper/test-reftable.c
+++ b/t/helper/test-reftable.c
@@ -13,7 +13,6 @@ int cmd__reftable(int argc, const char **argv)
 	readwrite_test_main(argc, argv);
 	merged_test_main(argc, argv);
 	stack_test_main(argc, argv);
-	refname_test_main(argc, argv);
 	return 0;
 }
 
-- 
2.44.GIT


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[PATCH v3 05/11] refs/reftable: don't recompute committer ident

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 6848 bytes --]

In order to write reflog entries we need to compute the committer's
identity as it gets encoded in the log record itself. The reftable
backend does this via `git_committer_info()` and `split_ident_line()` in
`fill_reftable_log_record()`, which use the Git config as well as
environment variables to figure out the identity.

While most callers would only call `fill_reftable_log_record()` once or
twice, `write_transaction_table()` will call it as many times as there
are queued ref updates. This can be quite a waste of effort when writing
many refs with reflog entries in a single transaction.

Refactor the code to pre-compute the committer information. This results
in a small speedup when writing 100000 refs in a single transaction:

  Benchmark 1: update-ref: create many refs (HEAD~)
    Time (mean ± σ):      2.895 s ±  0.020 s    [User: 1.516 s, System: 1.374 s]
    Range (min … max):    2.868 s …  2.983 s    100 runs

  Benchmark 2: update-ref: create many refs (HEAD)
    Time (mean ± σ):      2.845 s ±  0.017 s    [User: 1.461 s, System: 1.379 s]
    Range (min … max):    2.803 s …  2.913 s    100 runs

  Summary
    update-ref: create many refs (HEAD) ran
      1.02 ± 0.01 times faster than update-ref: create many refs (HEAD~)

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 refs/reftable-backend.c | 52 +++++++++++++++++++++++++++--------------
 1 file changed, 34 insertions(+), 18 deletions(-)

diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 8a54b0d8b2..a5ef36ffa9 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -171,32 +171,30 @@ static int should_write_log(struct ref_store *refs, const char *refname)
 	}
 }
 
-static void fill_reftable_log_record(struct reftable_log_record *log)
+static void fill_reftable_log_record(struct reftable_log_record *log, const struct ident_split *split)
 {
-	const char *info = git_committer_info(0);
-	struct ident_split split = {0};
+	const char *tz_begin;
 	int sign = 1;
 
-	if (split_ident_line(&split, info, strlen(info)))
-		BUG("failed splitting committer info");
-
 	reftable_log_record_release(log);
 	log->value_type = REFTABLE_LOG_UPDATE;
 	log->value.update.name =
-		xstrndup(split.name_begin, split.name_end - split.name_begin);
+		xstrndup(split->name_begin, split->name_end - split->name_begin);
 	log->value.update.email =
-		xstrndup(split.mail_begin, split.mail_end - split.mail_begin);
-	log->value.update.time = atol(split.date_begin);
-	if (*split.tz_begin == '-') {
+		xstrndup(split->mail_begin, split->mail_end - split->mail_begin);
+	log->value.update.time = atol(split->date_begin);
+
+	tz_begin = split->tz_begin;
+	if (*tz_begin == '-') {
 		sign = -1;
-		split.tz_begin++;
+		tz_begin++;
 	}
-	if (*split.tz_begin == '+') {
+	if (*tz_begin == '+') {
 		sign = 1;
-		split.tz_begin++;
+		tz_begin++;
 	}
 
-	log->value.update.tz_offset = sign * atoi(split.tz_begin);
+	log->value.update.tz_offset = sign * atoi(tz_begin);
 }
 
 static int read_ref_without_reload(struct reftable_stack *stack,
@@ -1018,9 +1016,15 @@ static int write_transaction_table(struct reftable_writer *writer, void *cb_data
 		reftable_stack_merged_table(arg->stack);
 	uint64_t ts = reftable_stack_next_update_index(arg->stack);
 	struct reftable_log_record *logs = NULL;
+	struct ident_split committer_ident = {0};
 	size_t logs_nr = 0, logs_alloc = 0, i;
+	const char *committer_info;
 	int ret = 0;
 
+	committer_info = git_committer_info(0);
+	if (split_ident_line(&committer_ident, committer_info, strlen(committer_info)))
+		BUG("failed splitting committer info");
+
 	QSORT(arg->updates, arg->updates_nr, transaction_update_cmp);
 
 	reftable_writer_set_limits(writer, ts, ts);
@@ -1086,7 +1090,7 @@ static int write_transaction_table(struct reftable_writer *writer, void *cb_data
 			log = &logs[logs_nr++];
 			memset(log, 0, sizeof(*log));
 
-			fill_reftable_log_record(log);
+			fill_reftable_log_record(log, &committer_ident);
 			log->update_index = ts;
 			log->refname = xstrdup(u->refname);
 			memcpy(log->value.update.new_hash, u->new_oid.hash, GIT_MAX_RAWSZ);
@@ -1233,9 +1237,11 @@ static int write_create_symref_table(struct reftable_writer *writer, void *cb_da
 		.value.symref = (char *)create->target,
 		.update_index = ts,
 	};
+	struct ident_split committer_ident = {0};
 	struct reftable_log_record log = {0};
 	struct object_id new_oid;
 	struct object_id old_oid;
+	const char *committer_info;
 	int ret;
 
 	reftable_writer_set_limits(writer, ts, ts);
@@ -1263,7 +1269,11 @@ static int write_create_symref_table(struct reftable_writer *writer, void *cb_da
 	    !should_write_log(&create->refs->base, create->refname))
 		return 0;
 
-	fill_reftable_log_record(&log);
+	committer_info = git_committer_info(0);
+	if (split_ident_line(&committer_ident, committer_info, strlen(committer_info)))
+		BUG("failed splitting committer info");
+
+	fill_reftable_log_record(&log, &committer_ident);
 	log.refname = xstrdup(create->refname);
 	log.update_index = ts;
 	log.value.update.message = xstrndup(create->logmsg,
@@ -1339,10 +1349,16 @@ static int write_copy_table(struct reftable_writer *writer, void *cb_data)
 	struct reftable_log_record old_log = {0}, *logs = NULL;
 	struct reftable_iterator it = {0};
 	struct string_list skip = STRING_LIST_INIT_NODUP;
+	struct ident_split committer_ident = {0};
 	struct strbuf errbuf = STRBUF_INIT;
 	size_t logs_nr = 0, logs_alloc = 0, i;
+	const char *committer_info;
 	int ret;
 
+	committer_info = git_committer_info(0);
+	if (split_ident_line(&committer_ident, committer_info, strlen(committer_info)))
+		BUG("failed splitting committer info");
+
 	if (reftable_stack_read_ref(arg->stack, arg->oldname, &old_ref)) {
 		ret = error(_("refname %s not found"), arg->oldname);
 		goto done;
@@ -1417,7 +1433,7 @@ static int write_copy_table(struct reftable_writer *writer, void *cb_data)
 
 		ALLOC_GROW(logs, logs_nr + 1, logs_alloc);
 		memset(&logs[logs_nr], 0, sizeof(logs[logs_nr]));
-		fill_reftable_log_record(&logs[logs_nr]);
+		fill_reftable_log_record(&logs[logs_nr], &committer_ident);
 		logs[logs_nr].refname = (char *)arg->newname;
 		logs[logs_nr].update_index = deletion_ts;
 		logs[logs_nr].value.update.message =
@@ -1449,7 +1465,7 @@ static int write_copy_table(struct reftable_writer *writer, void *cb_data)
 	 */
 	ALLOC_GROW(logs, logs_nr + 1, logs_alloc);
 	memset(&logs[logs_nr], 0, sizeof(logs[logs_nr]));
-	fill_reftable_log_record(&logs[logs_nr]);
+	fill_reftable_log_record(&logs[logs_nr], &committer_ident);
 	logs[logs_nr].refname = (char *)arg->newname;
 	logs[logs_nr].update_index = creation_ts;
 	logs[logs_nr].value.update.message =
-- 
2.44.GIT


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[PATCH v3 06/11] reftable/writer: refactorings for `writer_add_record()`

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 2566 bytes --]

Large parts of the reftable library do not conform to Git's typical code
style. Refactor `writer_add_record()` such that it conforms better to it
and add some documentation that explains some of its more intricate
behaviour.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 reftable/writer.c | 38 +++++++++++++++++++++++++++-----------
 1 file changed, 27 insertions(+), 11 deletions(-)

diff --git a/reftable/writer.c b/reftable/writer.c
index 1d9ff0fbfa..0ad5eb8887 100644
--- a/reftable/writer.c
+++ b/reftable/writer.c
@@ -209,7 +209,8 @@ static int writer_add_record(struct reftable_writer *w,
 			     struct reftable_record *rec)
 {
 	struct strbuf key = STRBUF_INIT;
-	int err = -1;
+	int err;
+
 	reftable_record_key(rec, &key);
 	if (strbuf_cmp(&w->last_key, &key) >= 0) {
 		err = REFTABLE_API_ERROR;
@@ -218,27 +219,42 @@ static int writer_add_record(struct reftable_writer *w,
 
 	strbuf_reset(&w->last_key);
 	strbuf_addbuf(&w->last_key, &key);
-	if (!w->block_writer) {
+	if (!w->block_writer)
 		writer_reinit_block_writer(w, reftable_record_type(rec));
-	}
 
-	assert(block_writer_type(w->block_writer) == reftable_record_type(rec));
+	if (block_writer_type(w->block_writer) != reftable_record_type(rec))
+		BUG("record of type %d added to writer of type %d",
+		    reftable_record_type(rec), block_writer_type(w->block_writer));
 
-	if (block_writer_add(w->block_writer, rec) == 0) {
+	/*
+	 * Try to add the record to the writer. If this succeeds then we're
+	 * done. Otherwise the block writer may have hit the block size limit
+	 * and needs to be flushed.
+	 */
+	if (!block_writer_add(w->block_writer, rec)) {
 		err = 0;
 		goto done;
 	}
 
+	/*
+	 * The current block is full, so we need to flush and reinitialize the
+	 * writer to start writing the next block.
+	 */
 	err = writer_flush_block(w);
-	if (err < 0) {
+	if (err < 0)
 		goto done;
-	}
-
 	writer_reinit_block_writer(w, reftable_record_type(rec));
+
+	/*
+	 * Try to add the record to the writer again. If this still fails then
+	 * the record does not fit into the block size.
+	 *
+	 * TODO: it would be great to have `block_writer_add()` return proper
+	 *       error codes so that we don't have to second-guess the failure
+	 *       mode here.
+	 */
 	err = block_writer_add(w->block_writer, rec);
-	if (err == -1) {
-		/* we are writing into memory, so an error can only mean it
-		 * doesn't fit. */
+	if (err) {
 		err = REFTABLE_ENTRY_TOO_BIG_ERROR;
 		goto done;
 	}
-- 
2.44.GIT


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[PATCH v3 07/11] reftable/writer: refactorings for `writer_flush_nonempty_block()`

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 3749 bytes --]

Large parts of the reftable library do not conform to Git's typical code
style. Refactor `writer_flush_nonempty_block()` such that it conforms
better to it and add some documentation that explains some of its more
intricate behaviour.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 reftable/writer.c | 72 +++++++++++++++++++++++++++++------------------
 1 file changed, 44 insertions(+), 28 deletions(-)

diff --git a/reftable/writer.c b/reftable/writer.c
index 0ad5eb8887..d347ec4cc6 100644
--- a/reftable/writer.c
+++ b/reftable/writer.c
@@ -659,58 +659,74 @@ static void writer_clear_index(struct reftable_writer *w)
 	w->index_cap = 0;
 }
 
-static const int debug = 0;
-
 static int writer_flush_nonempty_block(struct reftable_writer *w)
 {
+	struct reftable_index_record index_record = {
+		.last_key = STRBUF_INIT,
+	};
 	uint8_t typ = block_writer_type(w->block_writer);
-	struct reftable_block_stats *bstats =
-		writer_reftable_block_stats(w, typ);
-	uint64_t block_typ_off = (bstats->blocks == 0) ? w->next : 0;
-	int raw_bytes = block_writer_finish(w->block_writer);
-	int padding = 0;
-	int err = 0;
-	struct reftable_index_record ir = { .last_key = STRBUF_INIT };
+	struct reftable_block_stats *bstats;
+	int raw_bytes, padding = 0, err;
+	uint64_t block_typ_off;
+
+	/*
+	 * Finish the current block. This will cause the block writer to emit
+	 * restart points and potentially compress records in case we are
+	 * writing a log block.
+	 *
+	 * Note that this is still happening in memory.
+	 */
+	raw_bytes = block_writer_finish(w->block_writer);
 	if (raw_bytes < 0)
 		return raw_bytes;
 
-	if (!w->opts.unpadded && typ != BLOCK_TYPE_LOG) {
+	/*
+	 * By default, all records except for log records are padded to the
+	 * block size.
+	 */
+	if (!w->opts.unpadded && typ != BLOCK_TYPE_LOG)
 		padding = w->opts.block_size - raw_bytes;
-	}
 
-	if (block_typ_off > 0) {
+	bstats = writer_reftable_block_stats(w, typ);
+	block_typ_off = (bstats->blocks == 0) ? w->next : 0;
+	if (block_typ_off > 0)
 		bstats->offset = block_typ_off;
-	}
-
 	bstats->entries += w->block_writer->entries;
 	bstats->restarts += w->block_writer->restart_len;
 	bstats->blocks++;
 	w->stats.blocks++;
 
-	if (debug) {
-		fprintf(stderr, "block %c off %" PRIu64 " sz %d (%d)\n", typ,
-			w->next, raw_bytes,
-			get_be24(w->block + w->block_writer->header_off + 1));
-	}
-
-	if (w->next == 0) {
+	/*
+	 * If this is the first block we're writing to the table then we need
+	 * to also write the reftable header.
+	 */
+	if (!w->next)
 		writer_write_header(w, w->block);
-	}
 
 	err = padded_write(w, w->block, raw_bytes, padding);
 	if (err < 0)
 		return err;
 
+	/*
+	 * Add an index record for every block that we're writing. If we end up
+	 * having more than a threshold of index records we will end up writing
+	 * an index section in `writer_finish_section()`. Each index record
+	 * contains the last record key of the block it is indexing as well as
+	 * the offset of that block.
+	 *
+	 * Note that this also applies when flushing index blocks, in which
+	 * case we will end up with a multi-level index.
+	 */
 	REFTABLE_ALLOC_GROW(w->index, w->index_len + 1, w->index_cap);
-
-	ir.offset = w->next;
-	strbuf_reset(&ir.last_key);
-	strbuf_addbuf(&ir.last_key, &w->block_writer->last_key);
-	w->index[w->index_len] = ir;
-
+	index_record.offset = w->next;
+	strbuf_reset(&index_record.last_key);
+	strbuf_addbuf(&index_record.last_key, &w->block_writer->last_key);
+	w->index[w->index_len] = index_record;
 	w->index_len++;
+
 	w->next += padding + raw_bytes;
 	w->block_writer = NULL;
+
 	return 0;
 }
 
-- 
2.44.GIT


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[PATCH v3 08/11] reftable/writer: unify releasing memory

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 2112 bytes --]

There are two code paths which release memory of the reftable writer:

  - `reftable_writer_close()` releases internal state after it has
    written data.

  - `reftable_writer_free()` releases the block that was written to and
    the writer itself.

Both code paths free different parts of the writer, and consequently the
caller must make sure to call both. And while callers mostly do this
already, this falls apart when a write failure causes the caller to skip
calling `reftable_write_close()`.

Introduce a new function `reftable_writer_release()` that releases all
internal state and call it from both paths. Like this it is fine for the
caller to not call `reftable_writer_close()`.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 reftable/writer.c | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/reftable/writer.c b/reftable/writer.c
index d347ec4cc6..4eeb736445 100644
--- a/reftable/writer.c
+++ b/reftable/writer.c
@@ -149,11 +149,21 @@ void reftable_writer_set_limits(struct reftable_writer *w, uint64_t min,
 	w->max_update_index = max;
 }
 
+static void writer_release(struct reftable_writer *w)
+{
+	if (w) {
+		reftable_free(w->block);
+		w->block = NULL;
+		block_writer_release(&w->block_writer_data);
+		w->block_writer = NULL;
+		writer_clear_index(w);
+		strbuf_release(&w->last_key);
+	}
+}
+
 void reftable_writer_free(struct reftable_writer *w)
 {
-	if (!w)
-		return;
-	reftable_free(w->block);
+	writer_release(w);
 	reftable_free(w);
 }
 
@@ -643,16 +653,13 @@ int reftable_writer_close(struct reftable_writer *w)
 	}
 
 done:
-	/* free up memory. */
-	block_writer_release(&w->block_writer_data);
-	writer_clear_index(w);
-	strbuf_release(&w->last_key);
+	writer_release(w);
 	return err;
 }
 
 static void writer_clear_index(struct reftable_writer *w)
 {
-	for (size_t i = 0; i < w->index_len; i++)
+	for (size_t i = 0; w->index && i < w->index_len; i++)
 		strbuf_release(&w->index[i].last_key);
 	FREE_AND_NULL(w->index);
 	w->index_len = 0;
-- 
2.44.GIT


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[PATCH v3 09/11] reftable/writer: reset `last_key` instead of releasing it

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 1795 bytes --]

The reftable writer tracks the last key that it has written so that it
can properly compute the compressed prefix for the next record it is
about to write. This last key must be reset whenever we move on to write
the next block, which is done in `writer_reinit_block_writer()`. We do
this by calling `strbuf_release()` though, which needlessly deallocates
the underlying buffer.

Convert the code to use `strbuf_reset()` instead, which saves one
allocation per block we're about to write. This requires us to also
amend `reftable_writer_free()` to release the buffer's memory now as we
previously seemingly relied on `writer_reinit_block_writer()` to release
the memory for us. Releasing memory here is the right thing to do
anyway.

While at it, convert a callsite where we truncate the buffer by setting
its length to zero to instead use `strbuf_reset()`, too.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 reftable/writer.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/reftable/writer.c b/reftable/writer.c
index 4eeb736445..10eccaaa07 100644
--- a/reftable/writer.c
+++ b/reftable/writer.c
@@ -109,7 +109,7 @@ static void writer_reinit_block_writer(struct reftable_writer *w, uint8_t typ)
 		block_start = header_size(writer_version(w));
 	}
 
-	strbuf_release(&w->last_key);
+	strbuf_reset(&w->last_key);
 	block_writer_init(&w->block_writer_data, typ, w->block,
 			  w->opts.block_size, block_start,
 			  hash_size(w->opts.hash_id));
@@ -478,7 +478,7 @@ static int writer_finish_section(struct reftable_writer *w)
 	bstats->max_index_level = max_level;
 
 	/* Reinit lastKey, as the next section can start with any key. */
-	w->last_key.len = 0;
+	strbuf_reset(&w->last_key);
 
 	return 0;
 }
-- 
2.44.GIT


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[PATCH v3 10/11] reftable/block: reuse zstream when writing log blocks

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 5150 bytes --]

While most reftable blocks are written to disk as-is, blocks for log
records are compressed with zlib. To compress them we use `compress2()`,
which is a simple wrapper around the more complex `zstream` interface
that would require multiple function invocations.

One downside of this interface is that `compress2()` will reallocate
internal state of the `zstream` interface on every single invocation.
Consequently, as we call `compress2()` for every single log block which
we are about to write, this can lead to quite some memory allocation
churn.

Refactor the code so that the block writer reuses a `zstream`. This
significantly reduces the number of bytes allocated when writing many
refs in a single transaction, as demonstrated by the following benchmark
that writes 100k refs in a single transaction.

Before:

  HEAP SUMMARY:
      in use at exit: 671,931 bytes in 151 blocks
    total heap usage: 22,631,887 allocs, 22,631,736 frees, 1,854,670,793 bytes allocated

After:

  HEAP SUMMARY:
      in use at exit: 671,931 bytes in 151 blocks
    total heap usage: 22,620,528 allocs, 22,620,377 frees, 1,245,549,984 bytes allocated

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 reftable/block.c | 80 +++++++++++++++++++++++++++++++-----------------
 reftable/block.h |  1 +
 2 files changed, 53 insertions(+), 28 deletions(-)

diff --git a/reftable/block.c b/reftable/block.c
index 298e8c56b9..d182561b4d 100644
--- a/reftable/block.c
+++ b/reftable/block.c
@@ -76,6 +76,10 @@ void block_writer_init(struct block_writer *bw, uint8_t typ, uint8_t *buf,
 	bw->entries = 0;
 	bw->restart_len = 0;
 	bw->last_key.len = 0;
+	if (!bw->zstream) {
+		REFTABLE_CALLOC_ARRAY(bw->zstream, 1);
+		deflateInit(bw->zstream, 9);
+	}
 }
 
 uint8_t block_writer_type(struct block_writer *bw)
@@ -139,39 +143,57 @@ int block_writer_finish(struct block_writer *w)
 	w->next += 2;
 	put_be24(w->buf + 1 + w->header_off, w->next);
 
+	/*
+	 * Log records are stored zlib-compressed. Note that the compression
+	 * also spans over the restart points we have just written.
+	 */
 	if (block_writer_type(w) == BLOCK_TYPE_LOG) {
 		int block_header_skip = 4 + w->header_off;
-		uLongf src_len = w->next - block_header_skip;
-		uLongf dest_cap = src_len * 1.001 + 12;
-		uint8_t *compressed;
-
-		REFTABLE_ALLOC_ARRAY(compressed, dest_cap);
-
-		while (1) {
-			uLongf out_dest_len = dest_cap;
-			int zresult = compress2(compressed, &out_dest_len,
-						w->buf + block_header_skip,
-						src_len, 9);
-			if (zresult == Z_BUF_ERROR && dest_cap < LONG_MAX) {
-				dest_cap *= 2;
-				compressed =
-					reftable_realloc(compressed, dest_cap);
-				if (compressed)
-					continue;
-			}
-
-			if (Z_OK != zresult) {
-				reftable_free(compressed);
-				return REFTABLE_ZLIB_ERROR;
-			}
-
-			memcpy(w->buf + block_header_skip, compressed,
-			       out_dest_len);
-			w->next = out_dest_len + block_header_skip;
+		uLongf src_len = w->next - block_header_skip, compressed_len;
+		unsigned char *compressed;
+		int ret;
+
+		ret = deflateReset(w->zstream);
+		if (ret != Z_OK)
+			return REFTABLE_ZLIB_ERROR;
+
+		/*
+		 * Precompute the upper bound of how many bytes the compressed
+		 * data may end up with. Combined with `Z_FINISH`, `deflate()`
+		 * is guaranteed to return `Z_STREAM_END`.
+		 */
+		compressed_len = deflateBound(w->zstream, src_len);
+		REFTABLE_ALLOC_ARRAY(compressed, compressed_len);
+
+		w->zstream->next_out = compressed;
+		w->zstream->avail_out = compressed_len;
+		w->zstream->next_in = w->buf + block_header_skip;
+		w->zstream->avail_in = src_len;
+
+		/*
+		 * We want to perform all decompression in a single step, which
+		 * is why we can pass Z_FINISH here. As we have precomputed the
+		 * deflated buffer's size via `deflateBound()` this function is
+		 * guaranteed to succeed according to the zlib documentation.
+		 */
+		ret = deflate(w->zstream, Z_FINISH);
+		if (ret != Z_STREAM_END) {
 			reftable_free(compressed);
-			break;
+			return REFTABLE_ZLIB_ERROR;
 		}
+
+		/*
+		 * Overwrite the uncompressed data we have already written and
+		 * adjust the `next` pointer to point right after the
+		 * compressed data.
+		 */
+		memcpy(w->buf + block_header_skip, compressed,
+		       w->zstream->total_out);
+		w->next = w->zstream->total_out + block_header_skip;
+
+		reftable_free(compressed);
 	}
+
 	return w->next;
 }
 
@@ -480,6 +502,8 @@ int block_reader_seek(struct block_reader *br, struct block_iter *it,
 
 void block_writer_release(struct block_writer *bw)
 {
+	deflateEnd(bw->zstream);
+	FREE_AND_NULL(bw->zstream);
 	FREE_AND_NULL(bw->restarts);
 	strbuf_release(&bw->last_key);
 	/* the block is not owned. */
diff --git a/reftable/block.h b/reftable/block.h
index 47acc62c0a..1375957fc8 100644
--- a/reftable/block.h
+++ b/reftable/block.h
@@ -18,6 +18,7 @@ license that can be found in the LICENSE file or at
  * allocation overhead.
  */
 struct block_writer {
+	z_stream *zstream;
 	uint8_t *buf;
 	uint32_t block_size;
 
-- 
2.44.GIT


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[PATCH v3 11/11] reftable/block: reuse compressed array

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 3219 bytes --]

Similar to the preceding commit, let's reuse the `compressed` array that
we use to store compressed data in. This results in a small reduction in
memory allocations when writing many refs.

Before:

  HEAP SUMMARY:
      in use at exit: 671,931 bytes in 151 blocks
    total heap usage: 22,620,528 allocs, 22,620,377 frees, 1,245,549,984 bytes allocated

After:

  HEAP SUMMARY:
      in use at exit: 671,931 bytes in 151 blocks
    total heap usage: 22,618,257 allocs, 22,618,106 frees, 1,236,351,528 bytes allocated

So while the reduction in allocations isn't really all that big, it's a
low hanging fruit and thus there isn't much of a reason not to pick it.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 reftable/block.c | 14 +++++---------
 reftable/block.h |  3 +++
 2 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/reftable/block.c b/reftable/block.c
index d182561b4d..fd494876b7 100644
--- a/reftable/block.c
+++ b/reftable/block.c
@@ -150,7 +150,6 @@ int block_writer_finish(struct block_writer *w)
 	if (block_writer_type(w) == BLOCK_TYPE_LOG) {
 		int block_header_skip = 4 + w->header_off;
 		uLongf src_len = w->next - block_header_skip, compressed_len;
-		unsigned char *compressed;
 		int ret;
 
 		ret = deflateReset(w->zstream);
@@ -163,9 +162,9 @@ int block_writer_finish(struct block_writer *w)
 		 * is guaranteed to return `Z_STREAM_END`.
 		 */
 		compressed_len = deflateBound(w->zstream, src_len);
-		REFTABLE_ALLOC_ARRAY(compressed, compressed_len);
+		REFTABLE_ALLOC_GROW(w->compressed, compressed_len, w->compressed_cap);
 
-		w->zstream->next_out = compressed;
+		w->zstream->next_out = w->compressed;
 		w->zstream->avail_out = compressed_len;
 		w->zstream->next_in = w->buf + block_header_skip;
 		w->zstream->avail_in = src_len;
@@ -177,21 +176,17 @@ int block_writer_finish(struct block_writer *w)
 		 * guaranteed to succeed according to the zlib documentation.
 		 */
 		ret = deflate(w->zstream, Z_FINISH);
-		if (ret != Z_STREAM_END) {
-			reftable_free(compressed);
+		if (ret != Z_STREAM_END)
 			return REFTABLE_ZLIB_ERROR;
-		}
 
 		/*
 		 * Overwrite the uncompressed data we have already written and
 		 * adjust the `next` pointer to point right after the
 		 * compressed data.
 		 */
-		memcpy(w->buf + block_header_skip, compressed,
+		memcpy(w->buf + block_header_skip, w->compressed,
 		       w->zstream->total_out);
 		w->next = w->zstream->total_out + block_header_skip;
-
-		reftable_free(compressed);
 	}
 
 	return w->next;
@@ -505,6 +500,7 @@ void block_writer_release(struct block_writer *bw)
 	deflateEnd(bw->zstream);
 	FREE_AND_NULL(bw->zstream);
 	FREE_AND_NULL(bw->restarts);
+	FREE_AND_NULL(bw->compressed);
 	strbuf_release(&bw->last_key);
 	/* the block is not owned. */
 }
diff --git a/reftable/block.h b/reftable/block.h
index 1375957fc8..657498014c 100644
--- a/reftable/block.h
+++ b/reftable/block.h
@@ -19,6 +19,9 @@ license that can be found in the LICENSE file or at
  */
 struct block_writer {
 	z_stream *zstream;
+	unsigned char *compressed;
+	size_t compressed_cap;
+
 	uint8_t *buf;
 	uint32_t block_size;
 
-- 
2.44.GIT


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Re: [PATCH v3 00/11] reftable: optimize write performance

[Junio C Hamano]

Patrick Steinhardt <ps@pks.im> writes:

> this is the first version of my patch series that aims to optimize write
> performance with the reftable backend.
>
> Changes compared to v2:
>
>     - The series now deepends on ps/reftable-binsearch-update at
>       d51d8cc368 (reftable/block: avoid decoding keys when searching
>       restart points, 2024-04-03). This is to resolve a merge conflict
>       with that other series which has landed in "next" already.
>
>     - Dropped the "reftable_" prefix from newly introduced internal
>       reftable functions.

Well, since I resolved the conflict and my rerere database already
knows the resolution, you did not have to do the rebasing yourself.
After undoing the rebase and recreating the merge of this topic into
'seen', i.e. db20edbf (Merge branch 'ps/reftable-write-optim' into
jch, 2024-04-05), the difference I see between the previous version
and this iteration I see are the following.  Please tell me if that
is the only change you are expecting, and please yell at me if that
is not the case---it would serve as a sanity check of my previous
conflict resolution that will also be applied going forward.

Thanks, queued.

diff --git a/reftable/writer.c b/reftable/writer.c
index 32438e49b4..10eccaaa07 100644
--- a/reftable/writer.c
+++ b/reftable/writer.c
@@ -149,7 +149,7 @@ void reftable_writer_set_limits(struct reftable_writer *w, uint64_t min,
 	w->max_update_index = max;
 }
 
-static void reftable_writer_release(struct reftable_writer *w)
+static void writer_release(struct reftable_writer *w)
 {
 	if (w) {
 		reftable_free(w->block);
@@ -163,7 +163,7 @@ static void reftable_writer_release(struct reftable_writer *w)
 
 void reftable_writer_free(struct reftable_writer *w)
 {
-	reftable_writer_release(w);
+	writer_release(w);
 	reftable_free(w);
 }
 
@@ -653,7 +653,7 @@ int reftable_writer_close(struct reftable_writer *w)
 	}
 
 done:
-	reftable_writer_release(w);
+	writer_release(w);
 	return err;
 }
 

Re: [PATCH v3 00/11] reftable: optimize write performance

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 2281 bytes --]

On Mon, Apr 08, 2024 at 05:09:13PM -0700, Junio C Hamano wrote:
> Patrick Steinhardt <ps@pks.im> writes:
> 
> > this is the first version of my patch series that aims to optimize write
> > performance with the reftable backend.
> >
> > Changes compared to v2:
> >
> >     - The series now deepends on ps/reftable-binsearch-update at
> >       d51d8cc368 (reftable/block: avoid decoding keys when searching
> >       restart points, 2024-04-03). This is to resolve a merge conflict
> >       with that other series which has landed in "next" already.
> >
> >     - Dropped the "reftable_" prefix from newly introduced internal
> >       reftable functions.
> 
> Well, since I resolved the conflict and my rerere database already
> knows the resolution, you did not have to do the rebasing yourself.
> After undoing the rebase and recreating the merge of this topic into
> 'seen', i.e. db20edbf (Merge branch 'ps/reftable-write-optim' into
> jch, 2024-04-05), the difference I see between the previous version
> and this iteration I see are the following.  Please tell me if that
> is the only change you are expecting, and please yell at me if that
> is not the case---it would serve as a sanity check of my previous
> conflict resolution that will also be applied going forward.
> 
> Thanks, queued.

The resolution looks as expected to me. Thanks!

Patrick

> diff --git a/reftable/writer.c b/reftable/writer.c
> index 32438e49b4..10eccaaa07 100644
> --- a/reftable/writer.c
> +++ b/reftable/writer.c
> @@ -149,7 +149,7 @@ void reftable_writer_set_limits(struct reftable_writer *w, uint64_t min,
>  	w->max_update_index = max;
>  }
>  
> -static void reftable_writer_release(struct reftable_writer *w)
> +static void writer_release(struct reftable_writer *w)
>  {
>  	if (w) {
>  		reftable_free(w->block);
> @@ -163,7 +163,7 @@ static void reftable_writer_release(struct reftable_writer *w)
>  
>  void reftable_writer_free(struct reftable_writer *w)
>  {
> -	reftable_writer_release(w);
> +	writer_release(w);
>  	reftable_free(w);
>  }
>  
> @@ -653,7 +653,7 @@ int reftable_writer_close(struct reftable_writer *w)
>  	}
>  
>  done:
> -	reftable_writer_release(w);
> +	writer_release(w);
>  	return err;
>  }
>  

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