[PATCH 0/8] builtin/maintenance: use "geometric" strategy by default

[PATCH 0/8] builtin/maintenance: use "geometric" strategy by default

[Patrick Steinhardt]

Hi,

this series converts our default strategy used by git-maintenance(1)
from "gc" to "geometric". The aim of this is twofold:

  - It completes the conversion to a more flexible infrastructure for
    repository maintenance. git-maintenance(1) is structured around
    tasks that can be toggled on/off as needed, and this is a lot easier
    to extend going forward.

  - We start to use a more efficient repacking strategy by default,
    which should especially help large repositories out there.

Out of these two, I think that the first point is actually the more
important one.

Unfortunately, a lot of our tests are racy or will fail with the new
strategy. This is mostly because the new strategy may decide to optimize
data structures in cases where the old strategy didn't, and because the
tasks we perform might be different. The majority of this patch series
thus adapts our tests accordingly. The actual change is a one-line
change in the final commit.

I was a bit torn initially whether or not I want to make the geometric
strategy the default right away, or whether we might first want to use
"feature.experimental" as an additional step. I'm quite happy to adapt
the series accordingly, but for the initial version I thought it might
invite more discussions if I pick the nuclear option :)

Of course, no matter how we do this, it is still possible to revert back
to the old strategy by setting "maintenance.strategy=gc".

Thanks!

Patrick

---
Patrick Steinhardt (8):
      t: fix races caused by background maintenance
      t: disable maintenance where we verify object database structure
      t34xx: don't expire reflogs where it matters
      t5400: explicitly use "gc" strategy
      t5510: explicitly use "gc" strategy
      t6500: explicitly use "gc" strategy
      t7900: prepare for switch of the default strategy
      builtin/maintenance: use "geometric" strategy by default

 builtin/gc.c                            | 2 +-
 run-command.c                           | 2 +-
 t/t0081-find-pack.sh                    | 1 +
 t/t3404-rebase-interactive.sh           | 2 ++
 t/t3406-rebase-message.sh               | 3 +++
 t/t3431-rebase-fork-point.sh            | 2 ++
 t/t3432-rebase-fast-forward.sh          | 2 ++
 t/t5316-pack-delta-depth.sh             | 1 +
 t/t5319-multi-pack-index.sh             | 1 +
 t/t5326-multi-pack-bitmaps.sh           | 3 ++-
 t/t5327-multi-pack-bitmaps-rev.sh       | 3 ++-
 t/t5331-pack-objects-stdin.sh           | 2 ++
 t/t5332-multi-pack-reuse.sh             | 1 +
 t/t5334-incremental-multi-pack-index.sh | 1 +
 t/t5400-send-pack.sh                    | 1 +
 t/t5500-fetch-pack.sh                   | 3 ++-
 t/t5510-fetch.sh                        | 1 +
 t/t5616-partial-clone.sh                | 7 ++++---
 t/t6500-gc.sh                           | 1 +
 t/t7700-repack.sh                       | 3 +++
 t/t7900-maintenance.sh                  | 7 ++++++-
 t/test-lib.sh                           | 4 ++++
 22 files changed, 44 insertions(+), 9 deletions(-)


---
base-commit: 73fd77805fc6406f31c36212846d9e2541d19321
change-id: 20260218-b4-pks-maintenance-default-geometric-strategy-17fcedf92461

[PATCH 1/8] t: fix races caused by background maintenance

[Patrick Steinhardt]

Many Git commands spawn git-maintenance(1) to optimize the repository in
the background. By default, performing the maintenance is for most of
the part asynchronous: we fork the executable and then continue with the
rest of our business logic.

This is working as expected for our users, but this behaviour is
somewhat problematic for our test suite as this is inherently racy. We
have many tests that verify the on-disk state of repositories, and those
tests may easily race with our background maintenance. In a similar
fashion, we may end up with processes that "leak" out of a current test
case.

Until now this tends to not be much of a problem. Our maintenance uses
git-gc(1) by default, which knows to bail out in case there aren't
either too many packfiles or too many loose objects. So even if other
data structures would need to be optimized, we won't do so unless the
object database also needs optimizations.

This is about to change though, as a subsequent commit will switch to
the "geometric" maintenance strategy as a default. The consequence is
that we will run required optimizations even if the object database is
well-optimized. And this uncovers races between our test suite and
background maintenance all over the place.

Disabling maintenance outright in our test suite is not really an
option, as it would result in significantly divergence from the "real
world" and reduce our test coverage. But we've got an alternative up our
sleeves: we can ensure that garbage collection runs synchronously by
overriding the "maintenance.autoDetach" configuration.

Of course that also diverges from the real world, as we now stop testing
that background maintenance interacts in a benign way with normal Git
commands. But on the other hand this ensures that the maintenance itself
does not for example lead to data loss in a more reproducible way.

Another concern is that this would make execution of the test suite much
slower. But a quick benchmark on my machine demonstrates that this does
not seem to be the case:

    Benchmark 1: meson test (revision = HEAD~)
      Time (mean ± σ):     131.182 s ±  1.293 s    [User: 853.737 s, System: 1160.479 s]
      Range (min … max):   130.001 s … 132.563 s    3 runs

    Benchmark 2: meson test (revision = HEAD)
      Time (mean ± σ):     129.554 s ±  0.507 s    [User: 849.040 s, System: 1152.664 s]
      Range (min … max):   129.000 s … 129.994 s    3 runs

    Summary
      meson test (revision = HEAD) ran
        1.01 ± 0.01 times faster than meson test (revision = HEAD~)

Funny enough, it even seems as if this speeds up test execution ever so
slightly, but that may just as well be noise.

Introduce a new `GIT_TEST_MAINT_AUTO_DETACH` environment variable that
allows us to override the auto-detach behaviour and set that varibale in
our tests.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 run-command.c            | 2 +-
 t/t5616-partial-clone.sh | 6 +++---
 t/t7900-maintenance.sh   | 1 +
 t/test-lib.sh            | 4 ++++
 4 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/run-command.c b/run-command.c
index e3e02475cc..438a290d30 100644
--- a/run-command.c
+++ b/run-command.c
@@ -1828,7 +1828,7 @@ int prepare_auto_maintenance(int quiet, struct child_process *maint)
 	 */
 	if (repo_config_get_bool(the_repository, "maintenance.autodetach", &auto_detach) &&
 	    repo_config_get_bool(the_repository, "gc.autodetach", &auto_detach))
-		auto_detach = 1;
+		auto_detach = git_env_bool("GIT_TEST_MAINT_AUTO_DETACH", true);
 
 	maint->git_cmd = 1;
 	maint->close_object_store = 1;
diff --git a/t/t5616-partial-clone.sh b/t/t5616-partial-clone.sh
index 1e354e057f..d62760eb92 100755
--- a/t/t5616-partial-clone.sh
+++ b/t/t5616-partial-clone.sh
@@ -229,7 +229,7 @@ test_expect_success 'fetch --refetch triggers repacking' '
 
 	GIT_TRACE2_EVENT="$PWD/trace1.event" \
 	git -C pc1 fetch --refetch origin &&
-	test_subcommand git maintenance run --auto --no-quiet --detach <trace1.event &&
+	test_subcommand git maintenance run --auto --no-quiet --no-detach <trace1.event &&
 	grep \"param\":\"gc.autopacklimit\",\"value\":\"1\" trace1.event &&
 	grep \"param\":\"maintenance.incremental-repack.auto\",\"value\":\"-1\" trace1.event &&
 
@@ -238,7 +238,7 @@ test_expect_success 'fetch --refetch triggers repacking' '
 		-c gc.autoPackLimit=0 \
 		-c maintenance.incremental-repack.auto=1234 \
 		-C pc1 fetch --refetch origin &&
-	test_subcommand git maintenance run --auto --no-quiet --detach <trace2.event &&
+	test_subcommand git maintenance run --auto --no-quiet --no-detach <trace2.event &&
 	grep \"param\":\"gc.autopacklimit\",\"value\":\"0\" trace2.event &&
 	grep \"param\":\"maintenance.incremental-repack.auto\",\"value\":\"-1\" trace2.event &&
 
@@ -247,7 +247,7 @@ test_expect_success 'fetch --refetch triggers repacking' '
 		-c gc.autoPackLimit=1234 \
 		-c maintenance.incremental-repack.auto=0 \
 		-C pc1 fetch --refetch origin &&
-	test_subcommand git maintenance run --auto --no-quiet --detach <trace3.event &&
+	test_subcommand git maintenance run --auto --no-quiet --no-detach <trace3.event &&
 	grep \"param\":\"gc.autopacklimit\",\"value\":\"1\" trace3.event &&
 	grep \"param\":\"maintenance.incremental-repack.auto\",\"value\":\"0\" trace3.event
 '
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index 7cc0ce57f8..d11d6f8f15 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -6,6 +6,7 @@ test_description='git maintenance builtin'
 
 GIT_TEST_COMMIT_GRAPH=0
 GIT_TEST_MULTI_PACK_INDEX=0
+sane_unset GIT_TEST_MAINT_AUTO_DETACH
 
 test_lazy_prereq XMLLINT '
 	xmllint --version
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 0fb76f7d11..aa805a01ce 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -1947,6 +1947,10 @@ test_lazy_prereq COMPAT_HASH '
 GIT_TEST_MAINT_SCHEDULER="none:exit 1"
 export GIT_TEST_MAINT_SCHEDULER
 
+# Ensure that tests cannot race with background maintenance by default.
+GIT_TEST_MAINT_AUTO_DETACH="false"
+export GIT_TEST_MAINT_AUTO_DETACH
+
 # Does this platform support `git fsmonitor--daemon`
 #
 test_lazy_prereq FSMONITOR_DAEMON '

-- 
2.53.0.414.gf7e9f6c205.dirty

Re: [PATCH 1/8] t: fix races caused by background maintenance

[Justin Tobler]

On 26/02/20 11:15AM, Patrick Steinhardt wrote:
> Many Git commands spawn git-maintenance(1) to optimize the repository in
> the background. By default, performing the maintenance is for most of
> the part asynchronous: we fork the executable and then continue with the
> rest of our business logic.
> 
> This is working as expected for our users, but this behaviour is
> somewhat problematic for our test suite as this is inherently racy. We
> have many tests that verify the on-disk state of repositories, and those
> tests may easily race with our background maintenance. In a similar
> fashion, we may end up with processes that "leak" out of a current test
> case.
> 
> Until now this tends to not be much of a problem. Our maintenance uses
> git-gc(1) by default, which knows to bail out in case there aren't
> either too many packfiles or too many loose objects. So even if other
> data structures would need to be optimized, we won't do so unless the
> object database also needs optimizations.
> 
> This is about to change though, as a subsequent commit will switch to
> the "geometric" maintenance strategy as a default. The consequence is
> that we will run required optimizations even if the object database is
> well-optimized. And this uncovers races between our test suite and
> background maintenance all over the place.
> 
> Disabling maintenance outright in our test suite is not really an
> option, as it would result in significantly divergence from the "real

s/significantly/significant/

> world" and reduce our test coverage. But we've got an alternative up our
> sleeves: we can ensure that garbage collection runs synchronously by
> overriding the "maintenance.autoDetach" configuration.
> 
> Of course that also diverges from the real world, as we now stop testing
> that background maintenance interacts in a benign way with normal Git
> commands. But on the other hand this ensures that the maintenance itself
> does not for example lead to data loss in a more reproducible way.
> 
> Another concern is that this would make execution of the test suite much
> slower. But a quick benchmark on my machine demonstrates that this does
> not seem to be the case:
> 
>     Benchmark 1: meson test (revision = HEAD~)
>       Time (mean ± σ):     131.182 s ±  1.293 s    [User: 853.737 s, System: 1160.479 s]
>       Range (min … max):   130.001 s … 132.563 s    3 runs
> 
>     Benchmark 2: meson test (revision = HEAD)
>       Time (mean ± σ):     129.554 s ±  0.507 s    [User: 849.040 s, System: 1152.664 s]
>       Range (min … max):   129.000 s … 129.994 s    3 runs
> 
>     Summary
>       meson test (revision = HEAD) ran
>         1.01 ± 0.01 times faster than meson test (revision = HEAD~)
> 
> Funny enough, it even seems as if this speeds up test execution ever so
> slightly, but that may just as well be noise.
> 
> Introduce a new `GIT_TEST_MAINT_AUTO_DETACH` environment variable that
> allows us to override the auto-detach behaviour and set that varibale in

s/varibale/variable/

> our tests.
> 
> Signed-off-by: Patrick Steinhardt <ps@pks.im>
> ---
>  run-command.c            | 2 +-
>  t/t5616-partial-clone.sh | 6 +++---
>  t/t7900-maintenance.sh   | 1 +
>  t/test-lib.sh            | 4 ++++
>  4 files changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/run-command.c b/run-command.c
> index e3e02475cc..438a290d30 100644
> --- a/run-command.c
> +++ b/run-command.c
> @@ -1828,7 +1828,7 @@ int prepare_auto_maintenance(int quiet, struct child_process *maint)
>  	 */
>  	if (repo_config_get_bool(the_repository, "maintenance.autodetach", &auto_detach) &&
>  	    repo_config_get_bool(the_repository, "gc.autodetach", &auto_detach))
> -		auto_detach = 1;
> +		auto_detach = git_env_bool("GIT_TEST_MAINT_AUTO_DETACH", true);

So now if "maintenance.autodetach" and "gc.autodetach" are both not set,
we then check for the "GIT_TEST_MAINT_AUTO_DETACH" env before defaulting
to true. Looks good.

>  
>  	maint->git_cmd = 1;
>  	maint->close_object_store = 1;
[snip]
> diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
> index 7cc0ce57f8..d11d6f8f15 100755
> --- a/t/t7900-maintenance.sh
> +++ b/t/t7900-maintenance.sh
> @@ -6,6 +6,7 @@ test_description='git maintenance builtin'
>  
>  GIT_TEST_COMMIT_GRAPH=0
>  GIT_TEST_MULTI_PACK_INDEX=0
> +sane_unset GIT_TEST_MAINT_AUTO_DETACH

I assume here we are unsetting the env for testing purposes. It might be
nice to leave some sort of breadcrumb comment here to explain to future
readers.

>  test_lazy_prereq XMLLINT '
>  	xmllint --version
> diff --git a/t/test-lib.sh b/t/test-lib.sh
> index 0fb76f7d11..aa805a01ce 100644
> --- a/t/test-lib.sh
> +++ b/t/test-lib.sh
> @@ -1947,6 +1947,10 @@ test_lazy_prereq COMPAT_HASH '
>  GIT_TEST_MAINT_SCHEDULER="none:exit 1"
>  export GIT_TEST_MAINT_SCHEDULER
>  
> +# Ensure that tests cannot race with background maintenance by default.
> +GIT_TEST_MAINT_AUTO_DETACH="false"
> +export GIT_TEST_MAINT_AUTO_DETACH

Looks good.

-Justin

[PATCH 2/8] t: disable maintenance where we verify object database structure

[Patrick Steinhardt]

We have a couple of tests that explicitly verify the structure of the
object database. Naturally, this structure is dependent on whether or
not we run repository maintenance: if it decides to optimize the object
database the expected structure is likely to not materialize.

Explicitly disable auto-maintenance in such tests so that we are not
dependent on decisions made by our maintenance.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 t/t0081-find-pack.sh                    | 1 +
 t/t5316-pack-delta-depth.sh             | 1 +
 t/t5319-multi-pack-index.sh             | 1 +
 t/t5326-multi-pack-bitmaps.sh           | 3 ++-
 t/t5327-multi-pack-bitmaps-rev.sh       | 3 ++-
 t/t5331-pack-objects-stdin.sh           | 2 ++
 t/t5332-multi-pack-reuse.sh             | 1 +
 t/t5334-incremental-multi-pack-index.sh | 1 +
 t/t5500-fetch-pack.sh                   | 3 ++-
 t/t5616-partial-clone.sh                | 1 +
 t/t7700-repack.sh                       | 3 +++
 11 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/t/t0081-find-pack.sh b/t/t0081-find-pack.sh
index 5a628bf735..26f017422d 100755
--- a/t/t0081-find-pack.sh
+++ b/t/t0081-find-pack.sh
@@ -68,6 +68,7 @@ test_expect_success 'add more packfiles' '
 '
 
 test_expect_success 'add more commits (as loose objects)' '
+	test_config maintenance.auto false &&
 	test_commit six &&
 	test_commit seven &&
 
diff --git a/t/t5316-pack-delta-depth.sh b/t/t5316-pack-delta-depth.sh
index 03dfb7a61e..8a067a45cb 100755
--- a/t/t5316-pack-delta-depth.sh
+++ b/t/t5316-pack-delta-depth.sh
@@ -48,6 +48,7 @@ test_description='pack-objects breaks long cross-pack delta chains'
 # repeatedly-modified file to generate the delta chain).
 
 test_expect_success 'create series of packs' '
+	test_config maintenance.auto false &&
 	test-tool genrandom foo 4096 >content &&
 	prev= &&
 	for i in $(test_seq 1 10)
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index faae98c7e7..7672d599d4 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -1315,6 +1315,7 @@ test_expect_success 'bitmapped packs are stored via the BTMP chunk' '
 	git init repo &&
 	(
 		cd repo &&
+		git config set maintenance.auto false &&
 
 		for i in 1 2 3 4 5
 		do
diff --git a/t/t5326-multi-pack-bitmaps.sh b/t/t5326-multi-pack-bitmaps.sh
index 892aeb09e4..62bd973d92 100755
--- a/t/t5326-multi-pack-bitmaps.sh
+++ b/t/t5326-multi-pack-bitmaps.sh
@@ -93,7 +93,8 @@ test_midx_bitmap_cases () {
 	test_expect_success 'setup test_repository' '
 		rm -rf * .git &&
 		git init &&
-		git config pack.writeBitmapLookupTable '"$writeLookupTable"'
+		git config pack.writeBitmapLookupTable '"$writeLookupTable"' &&
+		git config maintenance.auto false
 	'
 
 	midx_bitmap_core
diff --git a/t/t5327-multi-pack-bitmaps-rev.sh b/t/t5327-multi-pack-bitmaps-rev.sh
index 9cac03a94b..cfa12de2a8 100755
--- a/t/t5327-multi-pack-bitmaps-rev.sh
+++ b/t/t5327-multi-pack-bitmaps-rev.sh
@@ -30,7 +30,8 @@ test_midx_bitmap_rev () {
 	test_expect_success 'setup bitmap config' '
 		rm -rf * .git &&
 		git init &&
-		git config pack.writeBitmapLookupTable '"$writeLookupTable"'
+		git config pack.writeBitmapLookupTable '"$writeLookupTable"' &&
+		git config maintenance.auto false
 	'
 
 	midx_bitmap_core rev
diff --git a/t/t5331-pack-objects-stdin.sh b/t/t5331-pack-objects-stdin.sh
index cd949025b9..b03f6be164 100755
--- a/t/t5331-pack-objects-stdin.sh
+++ b/t/t5331-pack-objects-stdin.sh
@@ -14,6 +14,7 @@ packed_objects () {
 
 test_expect_success 'setup for --stdin-packs tests' '
 	git init stdin-packs &&
+	git -C stdin-packs config set maintenance.auto false &&
 	(
 		cd stdin-packs &&
 
@@ -255,6 +256,7 @@ test_expect_success '--stdin-packs=follow walks into unknown packs' '
 	git init repo &&
 	(
 		cd repo &&
+		git config set maintenance.auto false &&
 
 		for c in A B C D
 		do
diff --git a/t/t5332-multi-pack-reuse.sh b/t/t5332-multi-pack-reuse.sh
index 395d09444c..881ce668e1 100755
--- a/t/t5332-multi-pack-reuse.sh
+++ b/t/t5332-multi-pack-reuse.sh
@@ -59,6 +59,7 @@ test_pack_objects_reused () {
 
 test_expect_success 'preferred pack is reused for single-pack reuse' '
 	test_config pack.allowPackReuse single &&
+	git config set maintenance.auto false &&
 
 	for i in A B
 	do
diff --git a/t/t5334-incremental-multi-pack-index.sh b/t/t5334-incremental-multi-pack-index.sh
index d30d7253d6..99c7d44d8e 100755
--- a/t/t5334-incremental-multi-pack-index.sh
+++ b/t/t5334-incremental-multi-pack-index.sh
@@ -15,6 +15,7 @@ midx_chain=$midxdir/multi-pack-index-chain
 
 test_expect_success 'convert non-incremental MIDX to incremental' '
 	test_commit base &&
+	git config set maintenance.auto false &&
 	git repack -ad &&
 	git multi-pack-index write &&
 
diff --git a/t/t5500-fetch-pack.sh b/t/t5500-fetch-pack.sh
index 4bb56c167a..0c88d04d0a 100755
--- a/t/t5500-fetch-pack.sh
+++ b/t/t5500-fetch-pack.sh
@@ -154,7 +154,8 @@ test_expect_success 'clone shallow depth 1 with fsck' '
 '
 
 test_expect_success 'clone shallow' '
-	git clone --no-single-branch --depth 2 "file://$(pwd)/." shallow
+	git clone --no-single-branch --depth 2 "file://$(pwd)/." shallow &&
+	git -C shallow config set maintenance.auto false
 '
 
 test_expect_success 'clone shallow depth count' '
diff --git a/t/t5616-partial-clone.sh b/t/t5616-partial-clone.sh
index d62760eb92..1c2805acca 100755
--- a/t/t5616-partial-clone.sh
+++ b/t/t5616-partial-clone.sh
@@ -585,6 +585,7 @@ test_expect_success 'verify fetch downloads only one pack when updating refs' '
 	git clone --filter=blob:none "file://$(pwd)/srv.bare" pack-test &&
 	ls pack-test/.git/objects/pack/*pack >pack-list &&
 	test_line_count = 2 pack-list &&
+	test_config -C pack-test maintenance.auto false &&
 	for i in A B C
 	do
 		test_commit -C src $i &&
diff --git a/t/t7700-repack.sh b/t/t7700-repack.sh
index 73b78bdd88..acc2589f21 100755
--- a/t/t7700-repack.sh
+++ b/t/t7700-repack.sh
@@ -217,6 +217,7 @@ test_expect_success 'repack --keep-pack' '
 		cd keep-pack &&
 		# avoid producing different packs due to delta/base choices
 		git config pack.window 0 &&
+		git config maintenance.auto false &&
 		P1=$(commit_and_pack 1) &&
 		P2=$(commit_and_pack 2) &&
 		P3=$(commit_and_pack 3) &&
@@ -260,6 +261,7 @@ test_expect_success 'repacking fails when missing .pack actually means missing o
 
 		# Avoid producing different packs due to delta/base choices
 		git config pack.window 0 &&
+		git config maintenance.auto false &&
 		P1=$(commit_and_pack 1) &&
 		P2=$(commit_and_pack 2) &&
 		P3=$(commit_and_pack 3) &&
@@ -534,6 +536,7 @@ test_expect_success 'setup for --write-midx tests' '
 	(
 		cd midx &&
 		git config core.multiPackIndex true &&
+		git config maintenance.auto false &&
 
 		test_commit base
 	)

-- 
2.53.0.414.gf7e9f6c205.dirty

Re: [PATCH 2/8] t: disable maintenance where we verify object database structure

[Justin Tobler]

On 26/02/20 11:15AM, Patrick Steinhardt wrote:
> We have a couple of tests that explicitly verify the structure of the
> object database. Naturally, this structure is dependent on whether or
> not we run repository maintenance: if it decides to optimize the object
> database the expected structure is likely to not materialize.
> 
> Explicitly disable auto-maintenance in such tests so that we are not
> dependent on decisions made by our maintenance.

I assume that these tests previously did not trigger maintenance to
begin with so now explicitly disabling maintenance does not change the
resulting structure. Changing the default to geometric repacking may
change this though.

-Justin

[PATCH 3/8] t34xx: don't expire reflogs where it matters

[Patrick Steinhardt]

We have a couple of tests in the t34xx range that rely on reflogs. This
never really used to be a problem, but in a subsequent commit we will
change the default maintenance strategy from "gc" to "geometric", and
this will cause us to drop all reflogs in these tests.

This may seem surprising and like a bug at first, but it's actually not.
The main difference between these two strategies is that the "gc"
strategy will skip all maintenance in case the object database is in a
well-optimized state. The "geometric" strategy has separate subtasks
though, and the conditions for each of these tasks is evaluated on a
case by case basis. This means that even if the object database is in
good shape, we may still decide to expire reflogs.

So why is that a problem? The issue is that Git's test suite hardcodes
the committer and author dates to a date in 2005. Interestingly though,
these hardcoded dates not only impact the commits, but also the reflog
entries. The consequence is that all newly written reflog entries are
immediately considered stale as our reflog expiration threshold is in
the range of weeks, only. It follows that executing `git reflog expire`
will thus immediately purge all reflog entries.

This hasn't been a problem in our test suite by pure chance, as the
repository shapes simply didn't cause us to perform actual garbage
collection. But with the upcoming "geometric" strategy we _will_ start
to execute `git reflog expire`, thus surfacing this issue.

Prepare for this by explicitly disabling reflog expiration in tests
impacted by this upcoming change.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 t/t3404-rebase-interactive.sh  | 2 ++
 t/t3406-rebase-message.sh      | 3 +++
 t/t3431-rebase-fork-point.sh   | 2 ++
 t/t3432-rebase-fast-forward.sh | 2 ++
 4 files changed, 9 insertions(+)

diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index e778dd8ae4..5e4623f7f1 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -31,6 +31,8 @@ Initial setup:
 . "$TEST_DIRECTORY"/lib-rebase.sh
 
 test_expect_success 'setup' '
+	git config set gc.reflogExpire never &&
+	git config set gc.reflogExpireUnreachable never &&
 	git switch -C primary &&
 	test_commit A file1 &&
 	test_commit B file1 &&
diff --git a/t/t3406-rebase-message.sh b/t/t3406-rebase-message.sh
index a1d7fa7f7c..f89209c8d9 100755
--- a/t/t3406-rebase-message.sh
+++ b/t/t3406-rebase-message.sh
@@ -8,6 +8,9 @@ export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 . ./test-lib.sh
 
 test_expect_success 'setup' '
+	git config set gc.reflogExpire never &&
+	git config set gc.reflogExpireUnreachable never &&
+
 	test_commit O fileO &&
 	test_commit X fileX &&
 	git branch fast-forward &&
diff --git a/t/t3431-rebase-fork-point.sh b/t/t3431-rebase-fork-point.sh
index be09fc78c1..3a3c3a70a5 100755
--- a/t/t3431-rebase-fork-point.sh
+++ b/t/t3431-rebase-fork-point.sh
@@ -17,6 +17,8 @@ export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 # C was formerly part of main but main was rewound to remove C
 #
 test_expect_success setup '
+	git config set gc.reflogExpire never &&
+	git config set gc.reflogExpireUnreachable never &&
 	test_commit A &&
 	test_commit B &&
 	test_commit C &&
diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index 5086e14c02..6e8de6c7aa 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -11,6 +11,8 @@ export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 . ./test-lib.sh
 
 test_expect_success setup '
+	git config set gc.reflogExpire never &&
+	git config set gc.reflogExpireUnreachable never &&
 	test_commit A &&
 	test_commit B &&
 	test_commit C &&

-- 
2.53.0.414.gf7e9f6c205.dirty

Re: [PATCH 3/8] t34xx: don't expire reflogs where it matters

[Derrick Stolee]

On 2/20/26 5:15 AM, Patrick Steinhardt wrote:
> We have a couple of tests in the t34xx range that rely on reflogs. This
> never really used to be a problem, but in a subsequent commit we will
> change the default maintenance strategy from "gc" to "geometric", and
> this will cause us to drop all reflogs in these tests.
> 
> This may seem surprising and like a bug at first, but it's actually not.
> The main difference between these two strategies is that the "gc"
> strategy will skip all maintenance in case the object database is in a
> well-optimized state. The "geometric" strategy has separate subtasks
> though, and the conditions for each of these tasks is evaluated on a
> case by case basis. This means that even if the object database is in
> good shape, we may still decide to expire reflogs.
> 
> So why is that a problem? The issue is that Git's test suite hardcodes
> the committer and author dates to a date in 2005. Interestingly though,
> these hardcoded dates not only impact the commits, but also the reflog
> entries. The consequence is that all newly written reflog entries are
> immediately considered stale as our reflog expiration threshold is in
> the range of weeks, only. It follows that executing `git reflog expire`
> will thus immediately purge all reflog entries.

I found these two paragraphs very valuable in explaining this patch.

Thanks!
-Stolee

Re: [PATCH 3/8] t34xx: don't expire reflogs where it matters

[Justin Tobler]

On 26/02/20 11:15AM, Patrick Steinhardt wrote:
> We have a couple of tests in the t34xx range that rely on reflogs. This
> never really used to be a problem, but in a subsequent commit we will
> change the default maintenance strategy from "gc" to "geometric", and
> this will cause us to drop all reflogs in these tests.
> 
> This may seem surprising and like a bug at first, but it's actually not.
> The main difference between these two strategies is that the "gc"
> strategy will skip all maintenance in case the object database is in a
> well-optimized state. The "geometric" strategy has separate subtasks
> though, and the conditions for each of these tasks is evaluated on a
> case by case basis. This means that even if the object database is in
> good shape, we may still decide to expire reflogs.
> 
> So why is that a problem? The issue is that Git's test suite hardcodes
> the committer and author dates to a date in 2005. Interestingly though,
> these hardcoded dates not only impact the commits, but also the reflog
> entries. The consequence is that all newly written reflog entries are
> immediately considered stale as our reflog expiration threshold is in
> the range of weeks, only. It follows that executing `git reflog expire`
> will thus immediately purge all reflog entries.
> 
> This hasn't been a problem in our test suite by pure chance, as the
> repository shapes simply didn't cause us to perform actual garbage
> collection. But with the upcoming "geometric" strategy we _will_ start
> to execute `git reflog expire`, thus surfacing this issue.

Interesting find.

> Prepare for this by explicitly disabling reflog expiration in tests
> impacted by this upcoming change.

Makes sense.

> Signed-off-by: Patrick Steinhardt <ps@pks.im>
> ---
>  t/t3404-rebase-interactive.sh  | 2 ++
>  t/t3406-rebase-message.sh      | 3 +++
>  t/t3431-rebase-fork-point.sh   | 2 ++
>  t/t3432-rebase-fast-forward.sh | 2 ++
>  4 files changed, 9 insertions(+)
> 
> diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
> index e778dd8ae4..5e4623f7f1 100755
> --- a/t/t3404-rebase-interactive.sh
> +++ b/t/t3404-rebase-interactive.sh
> @@ -31,6 +31,8 @@ Initial setup:
>  . "$TEST_DIRECTORY"/lib-rebase.sh
>  
>  test_expect_success 'setup' '
> +	git config set gc.reflogExpire never &&
> +	git config set gc.reflogExpireUnreachable never &&

As it may not be immediately obvious, it could be helpful for future
readers to explain in a comment that reflog dates are hardcoded to a
date that would be immediately expired and thus the need for this
configuration.

This patch looks good to me.

-Justin

[PATCH 4/8] t5400: explicitly use "gc" strategy

[Patrick Steinhardt]

In t5400 we verify that git-receive-pack(1) runs automated repository
maintenance in the remote repository. The check is performed indirectly
by observing an effect that git-gc(1) would have, namely to prune a
temporary object from the object database. In a subsequent commit we're
about to switch to the "geometric" strategy by default though, and here
we stop observing that effect.

Adapt the test to explicitly use the "gc" strategy to prepare for that
upcoming change.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 t/t5400-send-pack.sh | 1 +
 1 file changed, 1 insertion(+)

diff --git a/t/t5400-send-pack.sh b/t/t5400-send-pack.sh
index 83b42ff073..b32a0a6aa7 100755
--- a/t/t5400-send-pack.sh
+++ b/t/t5400-send-pack.sh
@@ -187,6 +187,7 @@ test_expect_success 'receive-pack runs auto-gc in remote repo' '
 		cd child &&
 		git config gc.autopacklimit 1 &&
 		git config gc.autodetach false &&
+		git config maintenance.strategy gc &&
 		git branch test_auto_gc &&
 		# And create a file that follows the temporary object naming
 		# convention for the auto-gc to remove

-- 
2.53.0.414.gf7e9f6c205.dirty

[PATCH 5/8] t5510: explicitly use "gc" strategy

[Patrick Steinhardt]

One of the tests in t5510 wants to verify that auto-gc does not lock up
when fetching into a repository. Adapt it to explicitly pick the "gc"
strategy for auto-maintenance.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 t/t5510-fetch.sh | 1 +
 1 file changed, 1 insertion(+)

diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
index c69afb5a60..5dcb4b51a4 100755
--- a/t/t5510-fetch.sh
+++ b/t/t5510-fetch.sh
@@ -1321,6 +1321,7 @@ test_expect_success 'fetching with auto-gc does not lock up' '
 		git config fetch.unpackLimit 1 &&
 		git config gc.autoPackLimit 1 &&
 		git config gc.autoDetach false &&
+		git config maintenance.strategy gc &&
 		GIT_ASK_YESNO="$TRASH_DIRECTORY/askyesno" git fetch --verbose >fetch.out 2>&1 &&
 		test_grep "Auto packing the repository" fetch.out &&
 		! grep "Should I try again" fetch.out

-- 
2.53.0.414.gf7e9f6c205.dirty

[PATCH 6/8] t6500: explicitly use "gc" strategy

[Patrick Steinhardt]

The test in t6500 explicitly wants to exercise git-gc(1) and is thus
highly specific to the actual on-disk state of the repository and
specifically of the object database. An upcoming change modifies the
default maintenance strategy to be the "geometric" strategy though,
which breaks a couple of assumptions.

One fix would arguably be to disable auto-maintenance altogether, as we
do want to explicitly verify git-gc(1) anyway. But as the whole test
suite is about git-gc(1) in the first place it feels more sensible to
configure the default maintenance strategy to be "gc".

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 t/t6500-gc.sh | 1 +
 1 file changed, 1 insertion(+)

diff --git a/t/t6500-gc.sh b/t/t6500-gc.sh
index bef472cb8d..ea9aaad470 100755
--- a/t/t6500-gc.sh
+++ b/t/t6500-gc.sh
@@ -11,6 +11,7 @@ test_expect_success 'setup' '
 	# behavior, make sure we always pack everything to one pack by
 	# default
 	git config gc.bigPackThreshold 2g &&
+	git config set --global maintenance.strategy gc &&
 	test_oid_init
 '
 

-- 
2.53.0.414.gf7e9f6c205.dirty

[PATCH 7/8] t7900: prepare for switch of the default strategy

[Patrick Steinhardt]

The t7900 test suite is exercising git-maintenance(1) and is thus of
course heavily reliant on the exact maintenance strategy. This reliance
comes in two flavors:

  - One test explicitly wants to verify that git-gc(1) is run as part of
    `git maintenance run`. This test is adapted by explicitly picking the
    "gc" strategy.

  - The other tests assume a specific shape of the object database,
    which is dependent on whether or not we run auto-maintenance before
    we come to the actual subject under test. These tests are adapted by
    disabling auto-maintenance.

With these changes t7900 passes with both "gc" and "geometric" default
strategies.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 t/t7900-maintenance.sh | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index d11d6f8f15..63276dcc5f 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -43,7 +43,8 @@ test_expect_success 'help text' '
 	test_grep "usage: git maintenance" err
 '
 
-test_expect_success 'run [--auto|--quiet]' '
+test_expect_success 'run [--auto|--quiet] with gc strategy' '
+	test_config maintenance.strategy gc &&
 	GIT_TRACE2_EVENT="$(pwd)/run-no-auto.txt" \
 		git maintenance run 2>/dev/null &&
 	GIT_TRACE2_EVENT="$(pwd)/run-auto.txt" \
@@ -497,6 +498,7 @@ test_expect_success 'maintenance.incremental-repack.auto' '
 	(
 		cd incremental-repack-true &&
 		git config core.multiPackIndex true &&
+		git config maintenance.auto false &&
 		run_incremental_repack_and_verify
 	)
 '
@@ -507,6 +509,7 @@ test_expect_success 'maintenance.incremental-repack.auto (when config is unset)'
 	(
 		cd incremental-repack-unset &&
 		test_unconfig core.multiPackIndex &&
+		git config maintenance.auto false &&
 		run_incremental_repack_and_verify
 	)
 '
@@ -617,6 +620,7 @@ test_expect_success 'geometric repacking with --auto' '
 	git init repo &&
 	(
 		cd repo &&
+		git config set maintenance.auto false &&
 
 		# An empty repository does not need repacking, except when
 		# explicitly told to do it.

-- 
2.53.0.414.gf7e9f6c205.dirty

[PATCH 8/8] builtin/maintenance: use "geometric" strategy by default

[Patrick Steinhardt]

The git-gc(1) command has been introduced in the early days of Git in
30f610b7b0 (Create 'git gc' to perform common maintenance operations.,
2006-12-27) as the main repository maintenance utility. And while the
tool has of course evolved since then to cover new parts, the basic
strategy it uses has never really changed much.

It is safe to say that since 2006 the Git ecosystem has changed quite a
bit. Repositories tend to be much larger nowadays than they have been
almost 20 years ago, and large parts of the industry went crazy for
monorepos (for various wildly different definitions of "monorepo"). So
the maintenance strategy we used back then may not be the best fit
nowadays anymore.

Arguably, most of the maintenance tasks that git-gc(1) does are still
perfectly fine today: repacking references, expiring various data
structures and things like tend to not cause huge problems. But the big
exception is the way we repack objects.

git-gc(1) by default uses a split strategy: it performs incremental
repacks by default, and then whenever we have too many packs we perform
a large all-into-one repack. This all-into-one repack is what is causing
problems nowadays, as it is an operation that is quite expensive. While
it is wasteful in small- and medium-sized repositories, in large repos
it may even be prohibitively expensive.

We have eventually introduced git-maintenance(1) that was slated as a
replacement for git-gc(1). In contrast to git-gc(1), it was much more
flexible as it is structured around configurable tasks and strategies.
And while it knows about the "incremental" strategy that we may use for
scheduled maintenance when configured via Scalar, its default still is
to use git-gc(1) in the background.

The "incremental" strategy isn't really a full replacement for git-gc(1)
though, as it doesn't know to expire unused data structures. In Git 2.52
we have thus introduced a new "geometric" strategy that is a proper
replacement for the old git-gc(1).

In contrast to the incremental/all-into-one split used by git-gc(1), the
new "geometric" strategy maintains a geometric progression of packfiles,
which significantly reduces the number of all-into-one repacks that we
have to perform in large repositories. It is thus a much better fit for
large repositories than git-gc(1).

Note that the "geometric" strategy isn't perfect though: while we
perform way less all-into-one repacks compared to git-gc(1), we still
have to perform them eventually. But for the largest repositories out
there this may not be an option, as client machines might not be
powerful enough to perform such a repack in the first place. These cases
would thus still be covered by Scalar's "incremental" strategy.

Switch the default strategy away from "gc" to "geometric", but retain
the "incremental" strategy configured by Scalar.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 builtin/gc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/builtin/gc.c b/builtin/gc.c
index 4390eee6ec..fb329c2cff 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -1980,7 +1980,7 @@ static void initialize_task_config(struct maintenance_run_opts *opts,
 		strategy = none_strategy;
 		type = MAINTENANCE_TYPE_SCHEDULED;
 	} else {
-		strategy = gc_strategy;
+		strategy = geometric_strategy;
 		type = MAINTENANCE_TYPE_MANUAL;
 	}
 

-- 
2.53.0.414.gf7e9f6c205.dirty

Re: [PATCH 8/8] builtin/maintenance: use "geometric" strategy by default

[Derrick Stolee]

On 2/20/26 5:15 AM, Patrick Steinhardt wrote:
> The git-gc(1) command has been introduced in the early days of Git in
> 30f610b7b0 (Create 'git gc' to perform common maintenance operations.,
> 2006-12-27) as the main repository maintenance utility. And while the
> tool has of course evolved since then to cover new parts, the basic
> strategy it uses has never really changed much.

I agree that the 'gc' strategy no longer serves users as a good default.
For those that want foreground commands to trigger maintenance (detached
on Unix, and as a blocking child on Windows) the 'geometric' strategy is
a good one.

> Switch the default strategy away from "gc" to "geometric", but retain
> the "incremental" strategy configured by Scalar.

Instead of "configured by Scalar" I'd say instead "configured when
initializing background maintenance with 'git maintenance start'" which
is how how Scalar sets this up indirectly.

Users could still opt-in to 'geometric' in the background, but it
would cause difficulties for the largest of repos that rely on the
'incremental' strategy's limit of the amount of data processed.

>   	} else {
> -		strategy = gc_strategy;
> +		strategy = geometric_strategy;
>   		type = MAINTENANCE_TYPE_MANUAL;
>   	}

Should this include some kind of documentation update in
Documentation/config/maintenance.adoc?

Thanks,
-Stolee

Re: [PATCH 8/8] builtin/maintenance: use "geometric" strategy by default

[Patrick Steinhardt]

On Sun, Feb 22, 2026 at 07:52:40PM -0500, Derrick Stolee wrote:
> On 2/20/26 5:15 AM, Patrick Steinhardt wrote:
> > The git-gc(1) command has been introduced in the early days of Git in
> > 30f610b7b0 (Create 'git gc' to perform common maintenance operations.,
> > 2006-12-27) as the main repository maintenance utility. And while the
> > tool has of course evolved since then to cover new parts, the basic
> > strategy it uses has never really changed much.
> 
> I agree that the 'gc' strategy no longer serves users as a good default.
> For those that want foreground commands to trigger maintenance (detached
> on Unix, and as a blocking child on Windows) the 'geometric' strategy is
> a good one.
> 
> > Switch the default strategy away from "gc" to "geometric", but retain
> > the "incremental" strategy configured by Scalar.
> 
> Instead of "configured by Scalar" I'd say instead "configured when
> initializing background maintenance with 'git maintenance start'" which
> is how how Scalar sets this up indirectly.
> 
> Users could still opt-in to 'geometric' in the background, but it
> would cause difficulties for the largest of repos that rely on the
> 'incremental' strategy's limit of the amount of data processed.

Makes sense, will rephrase.

> >   	} else {
> > -		strategy = gc_strategy;
> > +		strategy = geometric_strategy;
> >   		type = MAINTENANCE_TYPE_MANUAL;
> >   	}
> 
> Should this include some kind of documentation update in
> Documentation/config/maintenance.adoc?

Oh, right, it definitely should!

Patrick

Re: [PATCH 8/8] builtin/maintenance: use "geometric" strategy by default

[Justin Tobler]

On 26/02/20 11:15AM, Patrick Steinhardt wrote:
> The git-gc(1) command has been introduced in the early days of Git in
> 30f610b7b0 (Create 'git gc' to perform common maintenance operations.,
> 2006-12-27) as the main repository maintenance utility. And while the
> tool has of course evolved since then to cover new parts, the basic
> strategy it uses has never really changed much.
> 
> It is safe to say that since 2006 the Git ecosystem has changed quite a
> bit. Repositories tend to be much larger nowadays than they have been
> almost 20 years ago, and large parts of the industry went crazy for
> monorepos (for various wildly different definitions of "monorepo"). So
> the maintenance strategy we used back then may not be the best fit
> nowadays anymore.
> 
> Arguably, most of the maintenance tasks that git-gc(1) does are still
> perfectly fine today: repacking references, expiring various data
> structures and things like tend to not cause huge problems. But the big
> exception is the way we repack objects.
> 
> git-gc(1) by default uses a split strategy: it performs incremental
> repacks by default, and then whenever we have too many packs we perform
> a large all-into-one repack. This all-into-one repack is what is causing
> problems nowadays, as it is an operation that is quite expensive. While
> it is wasteful in small- and medium-sized repositories, in large repos
> it may even be prohibitively expensive.
> 
> We have eventually introduced git-maintenance(1) that was slated as a
> replacement for git-gc(1). In contrast to git-gc(1), it was much more
> flexible as it is structured around configurable tasks and strategies.
> And while it knows about the "incremental" strategy that we may use for
> scheduled maintenance when configured via Scalar, its default still is
> to use git-gc(1) in the background.

I'm a tad bit confused here. git-gc(1) by default uses an
"incremental/all-into-one" strategy and it is my understanding that this
is what git-maintenance(1) is currently using. Is there also another
"incremental" strategy for git-maintenance(1)?

> The "incremental" strategy isn't really a full replacement for git-gc(1)
> though, as it doesn't know to expire unused data structures. In Git 2.52
> we have thus introduced a new "geometric" strategy that is a proper
> replacement for the old git-gc(1).
> 
> In contrast to the incremental/all-into-one split used by git-gc(1), the
> new "geometric" strategy maintains a geometric progression of packfiles,
> which significantly reduces the number of all-into-one repacks that we
> have to perform in large repositories. It is thus a much better fit for
> large repositories than git-gc(1).
> 
> Note that the "geometric" strategy isn't perfect though: while we
> perform way less all-into-one repacks compared to git-gc(1), we still
> have to perform them eventually. But for the largest repositories out
> there this may not be an option, as client machines might not be
> powerful enough to perform such a repack in the first place. These cases
> would thus still be covered by Scalar's "incremental" strategy.

So the "problem" is the "all-into-one" repack. This ultimately occurs
for both the "gc" and "geometric" strategies so changing the default
strategy shouldn't make anything worse. Geometric repacking should in
fact delay the costly "all-into-one" repacks which is good.

> Switch the default strategy away from "gc" to "geometric", but retain
> the "incremental" strategy configured by Scalar.
> 
> Signed-off-by: Patrick Steinhardt <ps@pks.im>
> ---
>  builtin/gc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/builtin/gc.c b/builtin/gc.c
> index 4390eee6ec..fb329c2cff 100644
> --- a/builtin/gc.c
> +++ b/builtin/gc.c
> @@ -1980,7 +1980,7 @@ static void initialize_task_config(struct maintenance_run_opts *opts,
>  		strategy = none_strategy;
>  		type = MAINTENANCE_TYPE_SCHEDULED;
>  	} else {
> -		strategy = gc_strategy;
> +		strategy = geometric_strategy;

Looks good.

-Justin

Re: [PATCH 8/8] builtin/maintenance: use "geometric" strategy by default

[Patrick Steinhardt]

On Mon, Feb 23, 2026 at 10:48:59AM -0600, Justin Tobler wrote:
> On 26/02/20 11:15AM, Patrick Steinhardt wrote:
> > The git-gc(1) command has been introduced in the early days of Git in
> > 30f610b7b0 (Create 'git gc' to perform common maintenance operations.,
> > 2006-12-27) as the main repository maintenance utility. And while the
> > tool has of course evolved since then to cover new parts, the basic
> > strategy it uses has never really changed much.
> > 
> > It is safe to say that since 2006 the Git ecosystem has changed quite a
> > bit. Repositories tend to be much larger nowadays than they have been
> > almost 20 years ago, and large parts of the industry went crazy for
> > monorepos (for various wildly different definitions of "monorepo"). So
> > the maintenance strategy we used back then may not be the best fit
> > nowadays anymore.
> > 
> > Arguably, most of the maintenance tasks that git-gc(1) does are still
> > perfectly fine today: repacking references, expiring various data
> > structures and things like tend to not cause huge problems. But the big
> > exception is the way we repack objects.
> > 
> > git-gc(1) by default uses a split strategy: it performs incremental
> > repacks by default, and then whenever we have too many packs we perform
> > a large all-into-one repack. This all-into-one repack is what is causing
> > problems nowadays, as it is an operation that is quite expensive. While
> > it is wasteful in small- and medium-sized repositories, in large repos
> > it may even be prohibitively expensive.
> > 
> > We have eventually introduced git-maintenance(1) that was slated as a
> > replacement for git-gc(1). In contrast to git-gc(1), it was much more
> > flexible as it is structured around configurable tasks and strategies.
> > And while it knows about the "incremental" strategy that we may use for
> > scheduled maintenance when configured via Scalar, its default still is
> > to use git-gc(1) in the background.
> 
> I'm a tad bit confused here. git-gc(1) by default uses an
> "incremental/all-into-one" strategy and it is my understanding that this
> is what git-maintenance(1) is currently using. Is there also another
> "incremental" strategy for git-maintenance(1)?

There are three strategies right now:

  - "gc", which is the current default strategy that uses git-gc(1) to
    perform the incremental packs followed by the all-into-one repacks.

  - "incremental", which is set up by `git maintenance start`. This
    strategy never performs the all-into-one repacks, and it instead
    creates packs of a fixed upper size.

  - "geometric", which is the strategy that'll become the new default.

I'll try to clarify this a bit.

Patrick

Re: [PATCH 0/8] builtin/maintenance: use "geometric" strategy by default

[Derrick Stolee]

On 2/20/26 5:15 AM, Patrick Steinhardt wrote:
> Hi,
> 
> this series converts our default strategy used by git-maintenance(1)
> from "gc" to "geometric". The aim of this is twofold:
> 
>    - It completes the conversion to a more flexible infrastructure for
>      repository maintenance. git-maintenance(1) is structured around
>      tasks that can be toggled on/off as needed, and this is a lot easier
>      to extend going forward.
> 
>    - We start to use a more efficient repacking strategy by default,
>      which should especially help large repositories out there.
> 
> Out of these two, I think that the first point is actually the more
> important one.

I fully support this change as implemented, though I had a nit about
the final commit message and think there should be a documentation update
for this.

> Unfortunately, a lot of our tests are racy or will fail with the new
> strategy. This is mostly because the new strategy may decide to optimize
> data structures in cases where the old strategy didn't, and because the
> tasks we perform might be different. The majority of this patch series
> thus adapts our tests accordingly. The actual change is a one-line
> change in the final commit.

The patches that update these tests all look sensible. Thanks for the
extra care in explaining some tricky bits.

Thanks,
-Stolee

[PATCH v2 0/8] builtin/maintenance: use "geometric" strategy by default

[Patrick Steinhardt]

Hi,

this series converts our default strategy used by git-maintenance(1)
from "gc" to "geometric". The aim of this is twofold:

  - It completes the conversion to a more flexible infrastructure for
    repository maintenance. git-maintenance(1) is structured around
    tasks that can be toggled on/off as needed, and this is a lot easier
    to extend going forward.

  - We start to use a more efficient repacking strategy by default,
    which should especially help large repositories out there.

Out of these two, I think that the first point is actually the more
important one.

Unfortunately, a lot of our tests are racy or will fail with the new
strategy. This is mostly because the new strategy may decide to optimize
data structures in cases where the old strategy didn't, and because the
tasks we perform might be different. The majority of this patch series
thus adapts our tests accordingly. The actual change is a one-line
change in the final commit.

I was a bit torn initially whether or not I want to make the geometric
strategy the default right away, or whether we might first want to use
"feature.experimental" as an additional step. I'm quite happy to adapt
the series accordingly, but for the initial version I thought it might
invite more discussions if I pick the nuclear option :)

Of course, no matter how we do this, it is still possible to revert back
to the old strategy by setting "maintenance.strategy=gc".

Changes in v2:
  - Document the updated default strategy.
  - Clarify how this interacts with Scalar.
  - Explain the current landscape of strategies a bit better.
  - Leave some breadcrumbs in the tests.
  - Link to v1: https://lore.kernel.org/r/20260220-b4-pks-maintenance-default-geometric-strategy-v1-0-faeb321ad13b@pks.im

Thanks!

Patrick

---
Patrick Steinhardt (8):
      t: fix races caused by background maintenance
      t: disable maintenance where we verify object database structure
      t34xx: don't expire reflogs where it matters
      t5400: explicitly use "gc" strategy
      t5510: explicitly use "gc" strategy
      t6500: explicitly use "gc" strategy
      t7900: prepare for switch of the default strategy
      builtin/maintenance: use "geometric" strategy by default

 Documentation/config/maintenance.adoc   | 6 +++---
 builtin/gc.c                            | 2 +-
 run-command.c                           | 2 +-
 t/t0081-find-pack.sh                    | 1 +
 t/t3404-rebase-interactive.sh           | 6 ++++++
 t/t3406-rebase-message.sh               | 6 ++++++
 t/t3431-rebase-fork-point.sh            | 6 ++++++
 t/t3432-rebase-fast-forward.sh          | 6 ++++++
 t/t5316-pack-delta-depth.sh             | 1 +
 t/t5319-multi-pack-index.sh             | 1 +
 t/t5326-multi-pack-bitmaps.sh           | 3 ++-
 t/t5327-multi-pack-bitmaps-rev.sh       | 3 ++-
 t/t5331-pack-objects-stdin.sh           | 2 ++
 t/t5332-multi-pack-reuse.sh             | 1 +
 t/t5334-incremental-multi-pack-index.sh | 1 +
 t/t5400-send-pack.sh                    | 1 +
 t/t5500-fetch-pack.sh                   | 3 ++-
 t/t5510-fetch.sh                        | 1 +
 t/t5616-partial-clone.sh                | 7 ++++---
 t/t6500-gc.sh                           | 1 +
 t/t7700-repack.sh                       | 3 +++
 t/t7900-maintenance.sh                  | 9 ++++++++-
 t/test-lib.sh                           | 4 ++++
 23 files changed, 64 insertions(+), 12 deletions(-)

Range-diff versus v1:

1:  c5fadf42d0 ! 1:  9efc6d0a22 t: fix races caused by background maintenance
    @@ Commit message
         background maintenance all over the place.
     
         Disabling maintenance outright in our test suite is not really an
    -    option, as it would result in significantly divergence from the "real
    +    option, as it would result in significant divergence from the "real
         world" and reduce our test coverage. But we've got an alternative up our
         sleeves: we can ensure that garbage collection runs synchronously by
         overriding the "maintenance.autoDetach" configuration.
    @@ Commit message
         slightly, but that may just as well be noise.
     
         Introduce a new `GIT_TEST_MAINT_AUTO_DETACH` environment variable that
    -    allows us to override the auto-detach behaviour and set that varibale in
    +    allows us to override the auto-detach behaviour and set that variable in
         our tests.
     
         Signed-off-by: Patrick Steinhardt <ps@pks.im>
    @@ t/t5616-partial-clone.sh: test_expect_success 'fetch --refetch triggers repackin
     
      ## t/t7900-maintenance.sh ##
     @@ t/t7900-maintenance.sh: test_description='git maintenance builtin'
    - 
      GIT_TEST_COMMIT_GRAPH=0
      GIT_TEST_MULTI_PACK_INDEX=0
    -+sane_unset GIT_TEST_MAINT_AUTO_DETACH
      
    ++# Ensure that auto-maintenance detaches as usual.
    ++sane_unset GIT_TEST_MAINT_AUTO_DETACH
    ++
      test_lazy_prereq XMLLINT '
      	xmllint --version
    + '
     
      ## t/test-lib.sh ##
     @@ t/test-lib.sh: test_lazy_prereq COMPAT_HASH '
2:  805417a4a7 = 2:  f80bde1353 t: disable maintenance where we verify object database structure
3:  8a579a768d ! 3:  7087a68815 t34xx: don't expire reflogs where it matters
    @@ t/t3404-rebase-interactive.sh: Initial setup:
      . "$TEST_DIRECTORY"/lib-rebase.sh
      
      test_expect_success 'setup' '
    ++	# Commit dates are hardcoded to 2005, and the reflog entries will have
    ++	# a matching timestamp. Maintenance may thus immediately expire
    ++	# reflogs if it was running.
     +	git config set gc.reflogExpire never &&
     +	git config set gc.reflogExpireUnreachable never &&
    ++
      	git switch -C primary &&
      	test_commit A file1 &&
      	test_commit B file1 &&
    @@ t/t3406-rebase-message.sh: export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
      . ./test-lib.sh
      
      test_expect_success 'setup' '
    ++	# Commit dates are hardcoded to 2005, and the reflog entries will have
    ++	# a matching timestamp. Maintenance may thus immediately expire
    ++	# reflogs if it was running.
     +	git config set gc.reflogExpire never &&
     +	git config set gc.reflogExpireUnreachable never &&
     +
    @@ t/t3431-rebase-fork-point.sh: export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
      # C was formerly part of main but main was rewound to remove C
      #
      test_expect_success setup '
    ++	# Commit dates are hardcoded to 2005, and the reflog entries will have
    ++	# a matching timestamp. Maintenance may thus immediately expire
    ++	# reflogs if it was running.
     +	git config set gc.reflogExpire never &&
     +	git config set gc.reflogExpireUnreachable never &&
    ++
      	test_commit A &&
      	test_commit B &&
      	test_commit C &&
    @@ t/t3432-rebase-fast-forward.sh: export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
      . ./test-lib.sh
      
      test_expect_success setup '
    ++	# Commit dates are hardcoded to 2005, and the reflog entries will have
    ++	# a matching timestamp. Maintenance may thus immediately expire
    ++	# reflogs if it was running.
     +	git config set gc.reflogExpire never &&
     +	git config set gc.reflogExpireUnreachable never &&
    ++
      	test_commit A &&
      	test_commit B &&
      	test_commit C &&
4:  283143c1d8 = 4:  d230055b22 t5400: explicitly use "gc" strategy
5:  410dc16eb0 = 5:  dba219391f t5510: explicitly use "gc" strategy
6:  c4c8c5a7e4 = 6:  61bc1add2a t6500: explicitly use "gc" strategy
7:  93893cfee3 = 7:  b89505178d t7900: prepare for switch of the default strategy
8:  9e7aa390a5 < -:  ---------- builtin/maintenance: use "geometric" strategy by default
-:  ---------- > 8:  647d46a239 builtin/maintenance: use "geometric" strategy by default

---
base-commit: 73fd77805fc6406f31c36212846d9e2541d19321
change-id: 20260218-b4-pks-maintenance-default-geometric-strategy-17fcedf92461

[PATCH v2 1/8] t: fix races caused by background maintenance

[Patrick Steinhardt]

Many Git commands spawn git-maintenance(1) to optimize the repository in
the background. By default, performing the maintenance is for most of
the part asynchronous: we fork the executable and then continue with the
rest of our business logic.

This is working as expected for our users, but this behaviour is
somewhat problematic for our test suite as this is inherently racy. We
have many tests that verify the on-disk state of repositories, and those
tests may easily race with our background maintenance. In a similar
fashion, we may end up with processes that "leak" out of a current test
case.

Until now this tends to not be much of a problem. Our maintenance uses
git-gc(1) by default, which knows to bail out in case there aren't
either too many packfiles or too many loose objects. So even if other
data structures would need to be optimized, we won't do so unless the
object database also needs optimizations.

This is about to change though, as a subsequent commit will switch to
the "geometric" maintenance strategy as a default. The consequence is
that we will run required optimizations even if the object database is
well-optimized. And this uncovers races between our test suite and
background maintenance all over the place.

Disabling maintenance outright in our test suite is not really an
option, as it would result in significant divergence from the "real
world" and reduce our test coverage. But we've got an alternative up our
sleeves: we can ensure that garbage collection runs synchronously by
overriding the "maintenance.autoDetach" configuration.

Of course that also diverges from the real world, as we now stop testing
that background maintenance interacts in a benign way with normal Git
commands. But on the other hand this ensures that the maintenance itself
does not for example lead to data loss in a more reproducible way.

Another concern is that this would make execution of the test suite much
slower. But a quick benchmark on my machine demonstrates that this does
not seem to be the case:

    Benchmark 1: meson test (revision = HEAD~)
      Time (mean ± σ):     131.182 s ±  1.293 s    [User: 853.737 s, System: 1160.479 s]
      Range (min … max):   130.001 s … 132.563 s    3 runs

    Benchmark 2: meson test (revision = HEAD)
      Time (mean ± σ):     129.554 s ±  0.507 s    [User: 849.040 s, System: 1152.664 s]
      Range (min … max):   129.000 s … 129.994 s    3 runs

    Summary
      meson test (revision = HEAD) ran
        1.01 ± 0.01 times faster than meson test (revision = HEAD~)

Funny enough, it even seems as if this speeds up test execution ever so
slightly, but that may just as well be noise.

Introduce a new `GIT_TEST_MAINT_AUTO_DETACH` environment variable that
allows us to override the auto-detach behaviour and set that variable in
our tests.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 run-command.c            | 2 +-
 t/t5616-partial-clone.sh | 6 +++---
 t/t7900-maintenance.sh   | 3 +++
 t/test-lib.sh            | 4 ++++
 4 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/run-command.c b/run-command.c
index e3e02475cc..438a290d30 100644
--- a/run-command.c
+++ b/run-command.c
@@ -1828,7 +1828,7 @@ int prepare_auto_maintenance(int quiet, struct child_process *maint)
 	 */
 	if (repo_config_get_bool(the_repository, "maintenance.autodetach", &auto_detach) &&
 	    repo_config_get_bool(the_repository, "gc.autodetach", &auto_detach))
-		auto_detach = 1;
+		auto_detach = git_env_bool("GIT_TEST_MAINT_AUTO_DETACH", true);
 
 	maint->git_cmd = 1;
 	maint->close_object_store = 1;
diff --git a/t/t5616-partial-clone.sh b/t/t5616-partial-clone.sh
index 1e354e057f..d62760eb92 100755
--- a/t/t5616-partial-clone.sh
+++ b/t/t5616-partial-clone.sh
@@ -229,7 +229,7 @@ test_expect_success 'fetch --refetch triggers repacking' '
 
 	GIT_TRACE2_EVENT="$PWD/trace1.event" \
 	git -C pc1 fetch --refetch origin &&
-	test_subcommand git maintenance run --auto --no-quiet --detach <trace1.event &&
+	test_subcommand git maintenance run --auto --no-quiet --no-detach <trace1.event &&
 	grep \"param\":\"gc.autopacklimit\",\"value\":\"1\" trace1.event &&
 	grep \"param\":\"maintenance.incremental-repack.auto\",\"value\":\"-1\" trace1.event &&
 
@@ -238,7 +238,7 @@ test_expect_success 'fetch --refetch triggers repacking' '
 		-c gc.autoPackLimit=0 \
 		-c maintenance.incremental-repack.auto=1234 \
 		-C pc1 fetch --refetch origin &&
-	test_subcommand git maintenance run --auto --no-quiet --detach <trace2.event &&
+	test_subcommand git maintenance run --auto --no-quiet --no-detach <trace2.event &&
 	grep \"param\":\"gc.autopacklimit\",\"value\":\"0\" trace2.event &&
 	grep \"param\":\"maintenance.incremental-repack.auto\",\"value\":\"-1\" trace2.event &&
 
@@ -247,7 +247,7 @@ test_expect_success 'fetch --refetch triggers repacking' '
 		-c gc.autoPackLimit=1234 \
 		-c maintenance.incremental-repack.auto=0 \
 		-C pc1 fetch --refetch origin &&
-	test_subcommand git maintenance run --auto --no-quiet --detach <trace3.event &&
+	test_subcommand git maintenance run --auto --no-quiet --no-detach <trace3.event &&
 	grep \"param\":\"gc.autopacklimit\",\"value\":\"1\" trace3.event &&
 	grep \"param\":\"maintenance.incremental-repack.auto\",\"value\":\"0\" trace3.event
 '
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index 7cc0ce57f8..fe344f47ee 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -7,6 +7,9 @@ test_description='git maintenance builtin'
 GIT_TEST_COMMIT_GRAPH=0
 GIT_TEST_MULTI_PACK_INDEX=0
 
+# Ensure that auto-maintenance detaches as usual.
+sane_unset GIT_TEST_MAINT_AUTO_DETACH
+
 test_lazy_prereq XMLLINT '
 	xmllint --version
 '
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 0fb76f7d11..aa805a01ce 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -1947,6 +1947,10 @@ test_lazy_prereq COMPAT_HASH '
 GIT_TEST_MAINT_SCHEDULER="none:exit 1"
 export GIT_TEST_MAINT_SCHEDULER
 
+# Ensure that tests cannot race with background maintenance by default.
+GIT_TEST_MAINT_AUTO_DETACH="false"
+export GIT_TEST_MAINT_AUTO_DETACH
+
 # Does this platform support `git fsmonitor--daemon`
 #
 test_lazy_prereq FSMONITOR_DAEMON '

-- 
2.53.0.536.g309c995771.dirty

[PATCH v2 2/8] t: disable maintenance where we verify object database structure

[Patrick Steinhardt]

We have a couple of tests that explicitly verify the structure of the
object database. Naturally, this structure is dependent on whether or
not we run repository maintenance: if it decides to optimize the object
database the expected structure is likely to not materialize.

Explicitly disable auto-maintenance in such tests so that we are not
dependent on decisions made by our maintenance.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 t/t0081-find-pack.sh                    | 1 +
 t/t5316-pack-delta-depth.sh             | 1 +
 t/t5319-multi-pack-index.sh             | 1 +
 t/t5326-multi-pack-bitmaps.sh           | 3 ++-
 t/t5327-multi-pack-bitmaps-rev.sh       | 3 ++-
 t/t5331-pack-objects-stdin.sh           | 2 ++
 t/t5332-multi-pack-reuse.sh             | 1 +
 t/t5334-incremental-multi-pack-index.sh | 1 +
 t/t5500-fetch-pack.sh                   | 3 ++-
 t/t5616-partial-clone.sh                | 1 +
 t/t7700-repack.sh                       | 3 +++
 11 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/t/t0081-find-pack.sh b/t/t0081-find-pack.sh
index 5a628bf735..26f017422d 100755
--- a/t/t0081-find-pack.sh
+++ b/t/t0081-find-pack.sh
@@ -68,6 +68,7 @@ test_expect_success 'add more packfiles' '
 '
 
 test_expect_success 'add more commits (as loose objects)' '
+	test_config maintenance.auto false &&
 	test_commit six &&
 	test_commit seven &&
 
diff --git a/t/t5316-pack-delta-depth.sh b/t/t5316-pack-delta-depth.sh
index 03dfb7a61e..8a067a45cb 100755
--- a/t/t5316-pack-delta-depth.sh
+++ b/t/t5316-pack-delta-depth.sh
@@ -48,6 +48,7 @@ test_description='pack-objects breaks long cross-pack delta chains'
 # repeatedly-modified file to generate the delta chain).
 
 test_expect_success 'create series of packs' '
+	test_config maintenance.auto false &&
 	test-tool genrandom foo 4096 >content &&
 	prev= &&
 	for i in $(test_seq 1 10)
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index faae98c7e7..7672d599d4 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -1315,6 +1315,7 @@ test_expect_success 'bitmapped packs are stored via the BTMP chunk' '
 	git init repo &&
 	(
 		cd repo &&
+		git config set maintenance.auto false &&
 
 		for i in 1 2 3 4 5
 		do
diff --git a/t/t5326-multi-pack-bitmaps.sh b/t/t5326-multi-pack-bitmaps.sh
index 892aeb09e4..62bd973d92 100755
--- a/t/t5326-multi-pack-bitmaps.sh
+++ b/t/t5326-multi-pack-bitmaps.sh
@@ -93,7 +93,8 @@ test_midx_bitmap_cases () {
 	test_expect_success 'setup test_repository' '
 		rm -rf * .git &&
 		git init &&
-		git config pack.writeBitmapLookupTable '"$writeLookupTable"'
+		git config pack.writeBitmapLookupTable '"$writeLookupTable"' &&
+		git config maintenance.auto false
 	'
 
 	midx_bitmap_core
diff --git a/t/t5327-multi-pack-bitmaps-rev.sh b/t/t5327-multi-pack-bitmaps-rev.sh
index 9cac03a94b..cfa12de2a8 100755
--- a/t/t5327-multi-pack-bitmaps-rev.sh
+++ b/t/t5327-multi-pack-bitmaps-rev.sh
@@ -30,7 +30,8 @@ test_midx_bitmap_rev () {
 	test_expect_success 'setup bitmap config' '
 		rm -rf * .git &&
 		git init &&
-		git config pack.writeBitmapLookupTable '"$writeLookupTable"'
+		git config pack.writeBitmapLookupTable '"$writeLookupTable"' &&
+		git config maintenance.auto false
 	'
 
 	midx_bitmap_core rev
diff --git a/t/t5331-pack-objects-stdin.sh b/t/t5331-pack-objects-stdin.sh
index cd949025b9..b03f6be164 100755
--- a/t/t5331-pack-objects-stdin.sh
+++ b/t/t5331-pack-objects-stdin.sh
@@ -14,6 +14,7 @@ packed_objects () {
 
 test_expect_success 'setup for --stdin-packs tests' '
 	git init stdin-packs &&
+	git -C stdin-packs config set maintenance.auto false &&
 	(
 		cd stdin-packs &&
 
@@ -255,6 +256,7 @@ test_expect_success '--stdin-packs=follow walks into unknown packs' '
 	git init repo &&
 	(
 		cd repo &&
+		git config set maintenance.auto false &&
 
 		for c in A B C D
 		do
diff --git a/t/t5332-multi-pack-reuse.sh b/t/t5332-multi-pack-reuse.sh
index 395d09444c..881ce668e1 100755
--- a/t/t5332-multi-pack-reuse.sh
+++ b/t/t5332-multi-pack-reuse.sh
@@ -59,6 +59,7 @@ test_pack_objects_reused () {
 
 test_expect_success 'preferred pack is reused for single-pack reuse' '
 	test_config pack.allowPackReuse single &&
+	git config set maintenance.auto false &&
 
 	for i in A B
 	do
diff --git a/t/t5334-incremental-multi-pack-index.sh b/t/t5334-incremental-multi-pack-index.sh
index d30d7253d6..99c7d44d8e 100755
--- a/t/t5334-incremental-multi-pack-index.sh
+++ b/t/t5334-incremental-multi-pack-index.sh
@@ -15,6 +15,7 @@ midx_chain=$midxdir/multi-pack-index-chain
 
 test_expect_success 'convert non-incremental MIDX to incremental' '
 	test_commit base &&
+	git config set maintenance.auto false &&
 	git repack -ad &&
 	git multi-pack-index write &&
 
diff --git a/t/t5500-fetch-pack.sh b/t/t5500-fetch-pack.sh
index 4bb56c167a..0c88d04d0a 100755
--- a/t/t5500-fetch-pack.sh
+++ b/t/t5500-fetch-pack.sh
@@ -154,7 +154,8 @@ test_expect_success 'clone shallow depth 1 with fsck' '
 '
 
 test_expect_success 'clone shallow' '
-	git clone --no-single-branch --depth 2 "file://$(pwd)/." shallow
+	git clone --no-single-branch --depth 2 "file://$(pwd)/." shallow &&
+	git -C shallow config set maintenance.auto false
 '
 
 test_expect_success 'clone shallow depth count' '
diff --git a/t/t5616-partial-clone.sh b/t/t5616-partial-clone.sh
index d62760eb92..1c2805acca 100755
--- a/t/t5616-partial-clone.sh
+++ b/t/t5616-partial-clone.sh
@@ -585,6 +585,7 @@ test_expect_success 'verify fetch downloads only one pack when updating refs' '
 	git clone --filter=blob:none "file://$(pwd)/srv.bare" pack-test &&
 	ls pack-test/.git/objects/pack/*pack >pack-list &&
 	test_line_count = 2 pack-list &&
+	test_config -C pack-test maintenance.auto false &&
 	for i in A B C
 	do
 		test_commit -C src $i &&
diff --git a/t/t7700-repack.sh b/t/t7700-repack.sh
index 73b78bdd88..acc2589f21 100755
--- a/t/t7700-repack.sh
+++ b/t/t7700-repack.sh
@@ -217,6 +217,7 @@ test_expect_success 'repack --keep-pack' '
 		cd keep-pack &&
 		# avoid producing different packs due to delta/base choices
 		git config pack.window 0 &&
+		git config maintenance.auto false &&
 		P1=$(commit_and_pack 1) &&
 		P2=$(commit_and_pack 2) &&
 		P3=$(commit_and_pack 3) &&
@@ -260,6 +261,7 @@ test_expect_success 'repacking fails when missing .pack actually means missing o
 
 		# Avoid producing different packs due to delta/base choices
 		git config pack.window 0 &&
+		git config maintenance.auto false &&
 		P1=$(commit_and_pack 1) &&
 		P2=$(commit_and_pack 2) &&
 		P3=$(commit_and_pack 3) &&
@@ -534,6 +536,7 @@ test_expect_success 'setup for --write-midx tests' '
 	(
 		cd midx &&
 		git config core.multiPackIndex true &&
+		git config maintenance.auto false &&
 
 		test_commit base
 	)

-- 
2.53.0.536.g309c995771.dirty

[PATCH v2 3/8] t34xx: don't expire reflogs where it matters

[Patrick Steinhardt]

We have a couple of tests in the t34xx range that rely on reflogs. This
never really used to be a problem, but in a subsequent commit we will
change the default maintenance strategy from "gc" to "geometric", and
this will cause us to drop all reflogs in these tests.

This may seem surprising and like a bug at first, but it's actually not.
The main difference between these two strategies is that the "gc"
strategy will skip all maintenance in case the object database is in a
well-optimized state. The "geometric" strategy has separate subtasks
though, and the conditions for each of these tasks is evaluated on a
case by case basis. This means that even if the object database is in
good shape, we may still decide to expire reflogs.

So why is that a problem? The issue is that Git's test suite hardcodes
the committer and author dates to a date in 2005. Interestingly though,
these hardcoded dates not only impact the commits, but also the reflog
entries. The consequence is that all newly written reflog entries are
immediately considered stale as our reflog expiration threshold is in
the range of weeks, only. It follows that executing `git reflog expire`
will thus immediately purge all reflog entries.

This hasn't been a problem in our test suite by pure chance, as the
repository shapes simply didn't cause us to perform actual garbage
collection. But with the upcoming "geometric" strategy we _will_ start
to execute `git reflog expire`, thus surfacing this issue.

Prepare for this by explicitly disabling reflog expiration in tests
impacted by this upcoming change.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 t/t3404-rebase-interactive.sh  | 6 ++++++
 t/t3406-rebase-message.sh      | 6 ++++++
 t/t3431-rebase-fork-point.sh   | 6 ++++++
 t/t3432-rebase-fast-forward.sh | 6 ++++++
 4 files changed, 24 insertions(+)

diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index e778dd8ae4..3e44562afa 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -31,6 +31,12 @@ Initial setup:
 . "$TEST_DIRECTORY"/lib-rebase.sh
 
 test_expect_success 'setup' '
+	# Commit dates are hardcoded to 2005, and the reflog entries will have
+	# a matching timestamp. Maintenance may thus immediately expire
+	# reflogs if it was running.
+	git config set gc.reflogExpire never &&
+	git config set gc.reflogExpireUnreachable never &&
+
 	git switch -C primary &&
 	test_commit A file1 &&
 	test_commit B file1 &&
diff --git a/t/t3406-rebase-message.sh b/t/t3406-rebase-message.sh
index a1d7fa7f7c..bc51a9d3a7 100755
--- a/t/t3406-rebase-message.sh
+++ b/t/t3406-rebase-message.sh
@@ -8,6 +8,12 @@ export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 . ./test-lib.sh
 
 test_expect_success 'setup' '
+	# Commit dates are hardcoded to 2005, and the reflog entries will have
+	# a matching timestamp. Maintenance may thus immediately expire
+	# reflogs if it was running.
+	git config set gc.reflogExpire never &&
+	git config set gc.reflogExpireUnreachable never &&
+
 	test_commit O fileO &&
 	test_commit X fileX &&
 	git branch fast-forward &&
diff --git a/t/t3431-rebase-fork-point.sh b/t/t3431-rebase-fork-point.sh
index be09fc78c1..4336f417c2 100755
--- a/t/t3431-rebase-fork-point.sh
+++ b/t/t3431-rebase-fork-point.sh
@@ -17,6 +17,12 @@ export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 # C was formerly part of main but main was rewound to remove C
 #
 test_expect_success setup '
+	# Commit dates are hardcoded to 2005, and the reflog entries will have
+	# a matching timestamp. Maintenance may thus immediately expire
+	# reflogs if it was running.
+	git config set gc.reflogExpire never &&
+	git config set gc.reflogExpireUnreachable never &&
+
 	test_commit A &&
 	test_commit B &&
 	test_commit C &&
diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index 5086e14c02..181d19dcc1 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -11,6 +11,12 @@ export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 . ./test-lib.sh
 
 test_expect_success setup '
+	# Commit dates are hardcoded to 2005, and the reflog entries will have
+	# a matching timestamp. Maintenance may thus immediately expire
+	# reflogs if it was running.
+	git config set gc.reflogExpire never &&
+	git config set gc.reflogExpireUnreachable never &&
+
 	test_commit A &&
 	test_commit B &&
 	test_commit C &&

-- 
2.53.0.536.g309c995771.dirty

[PATCH v2 4/8] t5400: explicitly use "gc" strategy

[Patrick Steinhardt]

In t5400 we verify that git-receive-pack(1) runs automated repository
maintenance in the remote repository. The check is performed indirectly
by observing an effect that git-gc(1) would have, namely to prune a
temporary object from the object database. In a subsequent commit we're
about to switch to the "geometric" strategy by default though, and here
we stop observing that effect.

Adapt the test to explicitly use the "gc" strategy to prepare for that
upcoming change.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 t/t5400-send-pack.sh | 1 +
 1 file changed, 1 insertion(+)

diff --git a/t/t5400-send-pack.sh b/t/t5400-send-pack.sh
index 83b42ff073..b32a0a6aa7 100755
--- a/t/t5400-send-pack.sh
+++ b/t/t5400-send-pack.sh
@@ -187,6 +187,7 @@ test_expect_success 'receive-pack runs auto-gc in remote repo' '
 		cd child &&
 		git config gc.autopacklimit 1 &&
 		git config gc.autodetach false &&
+		git config maintenance.strategy gc &&
 		git branch test_auto_gc &&
 		# And create a file that follows the temporary object naming
 		# convention for the auto-gc to remove

-- 
2.53.0.536.g309c995771.dirty

[PATCH v2 5/8] t5510: explicitly use "gc" strategy

[Patrick Steinhardt]

One of the tests in t5510 wants to verify that auto-gc does not lock up
when fetching into a repository. Adapt it to explicitly pick the "gc"
strategy for auto-maintenance.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 t/t5510-fetch.sh | 1 +
 1 file changed, 1 insertion(+)

diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
index c69afb5a60..5dcb4b51a4 100755
--- a/t/t5510-fetch.sh
+++ b/t/t5510-fetch.sh
@@ -1321,6 +1321,7 @@ test_expect_success 'fetching with auto-gc does not lock up' '
 		git config fetch.unpackLimit 1 &&
 		git config gc.autoPackLimit 1 &&
 		git config gc.autoDetach false &&
+		git config maintenance.strategy gc &&
 		GIT_ASK_YESNO="$TRASH_DIRECTORY/askyesno" git fetch --verbose >fetch.out 2>&1 &&
 		test_grep "Auto packing the repository" fetch.out &&
 		! grep "Should I try again" fetch.out

-- 
2.53.0.536.g309c995771.dirty

[PATCH v2 6/8] t6500: explicitly use "gc" strategy

[Patrick Steinhardt]

The test in t6500 explicitly wants to exercise git-gc(1) and is thus
highly specific to the actual on-disk state of the repository and
specifically of the object database. An upcoming change modifies the
default maintenance strategy to be the "geometric" strategy though,
which breaks a couple of assumptions.

One fix would arguably be to disable auto-maintenance altogether, as we
do want to explicitly verify git-gc(1) anyway. But as the whole test
suite is about git-gc(1) in the first place it feels more sensible to
configure the default maintenance strategy to be "gc".

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 t/t6500-gc.sh | 1 +
 1 file changed, 1 insertion(+)

diff --git a/t/t6500-gc.sh b/t/t6500-gc.sh
index bef472cb8d..ea9aaad470 100755
--- a/t/t6500-gc.sh
+++ b/t/t6500-gc.sh
@@ -11,6 +11,7 @@ test_expect_success 'setup' '
 	# behavior, make sure we always pack everything to one pack by
 	# default
 	git config gc.bigPackThreshold 2g &&
+	git config set --global maintenance.strategy gc &&
 	test_oid_init
 '
 

-- 
2.53.0.536.g309c995771.dirty

Re: [PATCH v2 6/8] t6500: explicitly use "gc" strategy

[Toon Claes]

Patrick Steinhardt <ps@pks.im> writes:

> The test in t6500 explicitly wants to exercise git-gc(1) and is thus
> highly specific to the actual on-disk state of the repository and
> specifically of the object database. An upcoming change modifies the
> default maintenance strategy to be the "geometric" strategy though,
> which breaks a couple of assumptions.
>
> One fix would arguably be to disable auto-maintenance altogether, as we
> do want to explicitly verify git-gc(1) anyway. But as the whole test
> suite is about git-gc(1) in the first place it feels more sensible to
> configure the default maintenance strategy to be "gc".
>
> Signed-off-by: Patrick Steinhardt <ps@pks.im>
> ---
>  t/t6500-gc.sh | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/t/t6500-gc.sh b/t/t6500-gc.sh
> index bef472cb8d..ea9aaad470 100755
> --- a/t/t6500-gc.sh
> +++ b/t/t6500-gc.sh
> @@ -11,6 +11,7 @@ test_expect_success 'setup' '
>  	# behavior, make sure we always pack everything to one pack by
>  	# default
>  	git config gc.bigPackThreshold 2g &&
> +	git config set --global maintenance.strategy gc &&

I wasn't sure (no more) what effect setting globally would have. But
because each test file operates in it's own $TRASH_DIRECTORY, a global
setting only affects that file.

Makes sense.

-- 
Cheers,
Toon

[PATCH v2 7/8] t7900: prepare for switch of the default strategy

[Patrick Steinhardt]

The t7900 test suite is exercising git-maintenance(1) and is thus of
course heavily reliant on the exact maintenance strategy. This reliance
comes in two flavors:

  - One test explicitly wants to verify that git-gc(1) is run as part of
    `git maintenance run`. This test is adapted by explicitly picking the
    "gc" strategy.

  - The other tests assume a specific shape of the object database,
    which is dependent on whether or not we run auto-maintenance before
    we come to the actual subject under test. These tests are adapted by
    disabling auto-maintenance.

With these changes t7900 passes with both "gc" and "geometric" default
strategies.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 t/t7900-maintenance.sh | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index fe344f47ee..4700beacc1 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -45,7 +45,8 @@ test_expect_success 'help text' '
 	test_grep "usage: git maintenance" err
 '
 
-test_expect_success 'run [--auto|--quiet]' '
+test_expect_success 'run [--auto|--quiet] with gc strategy' '
+	test_config maintenance.strategy gc &&
 	GIT_TRACE2_EVENT="$(pwd)/run-no-auto.txt" \
 		git maintenance run 2>/dev/null &&
 	GIT_TRACE2_EVENT="$(pwd)/run-auto.txt" \
@@ -499,6 +500,7 @@ test_expect_success 'maintenance.incremental-repack.auto' '
 	(
 		cd incremental-repack-true &&
 		git config core.multiPackIndex true &&
+		git config maintenance.auto false &&
 		run_incremental_repack_and_verify
 	)
 '
@@ -509,6 +511,7 @@ test_expect_success 'maintenance.incremental-repack.auto (when config is unset)'
 	(
 		cd incremental-repack-unset &&
 		test_unconfig core.multiPackIndex &&
+		git config maintenance.auto false &&
 		run_incremental_repack_and_verify
 	)
 '
@@ -619,6 +622,7 @@ test_expect_success 'geometric repacking with --auto' '
 	git init repo &&
 	(
 		cd repo &&
+		git config set maintenance.auto false &&
 
 		# An empty repository does not need repacking, except when
 		# explicitly told to do it.

-- 
2.53.0.536.g309c995771.dirty

[PATCH v2 8/8] builtin/maintenance: use "geometric" strategy by default

[Patrick Steinhardt]

The git-gc(1) command has been introduced in the early days of Git in
30f610b7b0 (Create 'git gc' to perform common maintenance operations.,
2006-12-27) as the main repository maintenance utility. And while the
tool has of course evolved since then to cover new parts, the basic
strategy it uses has never really changed much.

It is safe to say that since 2006 the Git ecosystem has changed quite a
bit. Repositories tend to be much larger nowadays than they have been
almost 20 years ago, and large parts of the industry went crazy for
monorepos (for various wildly different definitions of "monorepo"). So
the maintenance strategy we used back then may not be the best fit
nowadays anymore.

Arguably, most of the maintenance tasks that git-gc(1) does are still
perfectly fine today: repacking references, expiring various data
structures and things like tend to not cause huge problems. But the big
exception is the way we repack objects.

git-gc(1) by default uses a split strategy: it performs incremental
repacks by default, and then whenever we have too many packs we perform
a large all-into-one repack. This all-into-one repack is what is causing
problems nowadays, as it is an operation that is quite expensive. While
it is wasteful in small- and medium-sized repositories, in large repos
it may even be prohibitively expensive.

We have eventually introduced git-maintenance(1) that was slated as a
replacement for git-gc(1). In contrast to git-gc(1), it is much more
flexible as it is structured around configurable tasks and strategies.
So while its default "gc" strategy still uses git-gc(1) under the hood,
it allows us to iterate.

A second strategy it knows about is the "incremental" strategy, which we
configure when registering a repository for scheduled maintenance. This
strategy isn't really a full replacement for git-gc(1) though, as it
doesn't know to expire unused data structures. In Git 2.52 we have thus
introduced a new "geometric" strategy that is a proper replacement for
the old git-gc(1).

In contrast to the incremental/all-into-one split used by git-gc(1), the
new "geometric" strategy maintains a geometric progression of packfiles,
which significantly reduces the number of all-into-one repacks that we
have to perform in large repositories. It is thus a much better fit for
large repositories than git-gc(1).

Note that the "geometric" strategy isn't perfect though: while we
perform way less all-into-one repacks compared to git-gc(1), we still
have to perform them eventually. But for the largest repositories out
there this may not be an option either, as client machines might not be
powerful enough to perform such a repack in the first place. These cases
would thus still be covered by the "incremental" strategy.

Switch the default strategy away from "gc" to "geometric", but retain
the "incremental" strategy configured when registering background
maintenance with `git maintenance register`.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 Documentation/config/maintenance.adoc | 6 +++---
 builtin/gc.c                          | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/Documentation/config/maintenance.adoc b/Documentation/config/maintenance.adoc
index d0c38f03fa..b578856dde 100644
--- a/Documentation/config/maintenance.adoc
+++ b/Documentation/config/maintenance.adoc
@@ -30,8 +30,7 @@ The possible strategies are:
 +
 * `none`: This strategy implies no tasks are run at all. This is the default
   strategy for scheduled maintenance.
-* `gc`: This strategy runs the `gc` task. This is the default strategy for
-  manual maintenance.
+* `gc`: This strategy runs the `gc` task.
 * `geometric`: This strategy performs geometric repacking of packfiles and
   keeps auxiliary data structures up-to-date. The strategy expires data in the
   reflog and removes worktrees that cannot be located anymore. When the
@@ -40,7 +39,8 @@ The possible strategies are:
   are already part of a cruft pack will be expired.
 +
 This repacking strategy is a full replacement for the `gc` strategy and is
-recommended for large repositories.
+recommended for large repositories. This is the default strategy for manual
+maintenance.
 * `incremental`: This setting optimizes for performing small maintenance
   activities that do not delete any data. This does not schedule the `gc`
   task, but runs the `prefetch` and `commit-graph` tasks hourly, the
diff --git a/builtin/gc.c b/builtin/gc.c
index 4390eee6ec..fb329c2cff 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -1980,7 +1980,7 @@ static void initialize_task_config(struct maintenance_run_opts *opts,
 		strategy = none_strategy;
 		type = MAINTENANCE_TYPE_SCHEDULED;
 	} else {
-		strategy = gc_strategy;
+		strategy = geometric_strategy;
 		type = MAINTENANCE_TYPE_MANUAL;
 	}
 

-- 
2.53.0.536.g309c995771.dirty

Re: [PATCH v2 8/8] builtin/maintenance: use "geometric" strategy by default

[Derrick Stolee]

On 2/24/26 3:45 AM, Patrick Steinhardt wrote:

> @@ -30,8 +30,7 @@ The possible strategies are:
>   +
>   * `none`: This strategy implies no tasks are run at all. This is the default
>     strategy for scheduled maintenance.
> -* `gc`: This strategy runs the `gc` task. This is the default strategy for
> -  manual maintenance.
> +* `gc`: This strategy runs the `gc` task.
>   * `geometric`: This strategy performs geometric repacking of packfiles and
>     keeps auxiliary data structures up-to-date. The strategy expires data in the
>     reflog and removes worktrees that cannot be located anymore. When the
> @@ -40,7 +39,8 @@ The possible strategies are:
>     are already part of a cruft pack will be expired.
>   +
>   This repacking strategy is a full replacement for the `gc` strategy and is
> -recommended for large repositories.
> +recommended for large repositories. This is the default strategy for manual
> +maintenance.

Thanks for these updates.

With this, v2 looks good to me.

-Stolee

Re: [PATCH v2 8/8] builtin/maintenance: use "geometric" strategy by default

[Toon Claes]

Derrick Stolee <stolee@gmail.com> writes:

> With this, v2 looks good to me.
>
> -Stolee
>

Also did a review on v2, and I've got no comments about it. Approving.

-- 
Cheers,
Toon

Re: [PATCH v2 0/8] builtin/maintenance: use "geometric" strategy by default

[Justin Tobler]

On 26/02/24 09:45AM, Patrick Steinhardt wrote:
> Changes in v2:
>   - Document the updated default strategy.
>   - Clarify how this interacts with Scalar.
>   - Explain the current landscape of strategies a bit better.
>   - Leave some breadcrumbs in the tests.
>   - Link to v1: https://lore.kernel.org/r/20260220-b4-pks-maintenance-default-geometric-strategy-v1-0-faeb321ad13b@pks.im

Thanks Patrick. This version addresses all my previous comments and
looks good to me.

-Justin