Re: [PATCH] repack: add `repack.honorpackkeep` config var

[Jeff King <peff@peff.net>]

On Thu, Feb 27, 2014 at 10:04:44AM -0800, Junio C Hamano wrote:

> I wonder if it makes sense to link it with "pack.writebitmaps" more
> tightly, without even exposing it as a seemingly orthogonal knob
> that can be tweaked, though.
> 
> I think that is because I do not fully understand the ", because ..."
> part of the below:
> 
> >> This patch introduces an option to disable the
> >> `--honor-pack-keep` option.  It is not triggered by default,
> >> even when pack.writeBitmaps is turned on, because its use
> >> depends on your overall packing strategy and use of .keep
> >> files.
> 
> If you ask --write-bitmap-index (or have pack.writeBitmaps on), you
> do want the bitmap-index to be written, and unless you tell
> pack-objects to ignore the .keep marker, it cannot do so, no?
> 
> Does the ", because ..." part above mean "you may have an overall
> packing strategy to use .keep file to not ever repack some subset of
> the objects, so we will not silently explode the kept objects into a
> new pack"?

Exactly. The two features (bitmaps and .keep) are not compatible with
each other, so you have to prioritize one. If you are using static .keep
files, you might want them to continue being respected at the expense of
using bitmaps for that repo. So I think you want a separate option from
--write-bitmap-index to allow the appropriate flexibility.

The default is another matter.  I think most people using .bitmaps on a
server would probably want to set repack.packKeptObjects.  They would
want to repack often to take advantage of the .bitmaps anyway, so they
probably don't care about .keep files (any they see are due to races
with incoming pushes).

So we could do something like falling back to turning the option on if
--write-bitmap-index is on _and_ the user didn't specify
--pack-kept-objects. The existing default is mostly there because it is
the conservative choice (.keep files continue to do their thing as
normal unless you say otherwise). But the fallback thing would be one
less knob that bitmap users would need to turn in the common case.

Here's the interdiff for doing the fallback:

---
diff --git a/Documentation/config.txt b/Documentation/config.txt
index 3a3d84f..a8ddc7f 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -2139,7 +2139,9 @@ repack.usedeltabaseoffset::
 repack.packKeptObjects::
 	If set to true, makes `git repack` act as if
 	`--pack-kept-objects` was passed. See linkgit:git-repack[1] for
-	details. Defaults to false.
+	details. Defaults to `false` normally, but `true` if a bitmap
+	index is being written (either via `--write-bitmap-index` or
+	`pack.writeBitmaps`).
 
 rerere.autoupdate::
 	When set to true, `git-rerere` updates the index with the
diff --git a/builtin/repack.c b/builtin/repack.c
index 49947b2..6b0b62d 100644
--- a/builtin/repack.c
+++ b/builtin/repack.c
@@ -9,7 +9,7 @@
 #include "argv-array.h"
 
 static int delta_base_offset = 1;
-static int pack_kept_objects;
+static int pack_kept_objects = -1;
 static char *packdir, *packtmp;
 
 static const char *const git_repack_usage[] = {
@@ -190,6 +190,9 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 	argc = parse_options(argc, argv, prefix, builtin_repack_options,
 				git_repack_usage, 0);
 
+	if (pack_kept_objects < 0)
+		pack_kept_objects = write_bitmap;
+
 	packdir = mkpathdup("%s/pack", get_object_directory());
 	packtmp = mkpathdup("%s/.tmp-%d-pack", packdir, (int)getpid());
 
diff --git a/t/t7700-repack.sh b/t/t7700-repack.sh
index f8431a8..b1eed5c 100755
--- a/t/t7700-repack.sh
+++ b/t/t7700-repack.sh
@@ -21,7 +21,7 @@ test_expect_success 'objects in packs marked .keep are not repacked' '
 	objsha1=$(git verify-pack -v pack-$packsha1.idx | head -n 1 |
 		sed -e "s/^\([0-9a-f]\{40\}\).*/\1/") &&
 	mv pack-* .git/objects/pack/ &&
-	git repack -A -d -l &&
+	git repack --no-pack-kept-objects -A -d -l &&
 	git prune-packed &&
 	for p in .git/objects/pack/*.idx; do
 		idx=$(basename $p)
@@ -35,9 +35,9 @@ test_expect_success 'objects in packs marked .keep are not repacked' '
 	test -z "$found_duplicate_object"
 '
 
-test_expect_success '--pack-kept-objects duplicates objects' '
+test_expect_success 'writing bitmaps duplicates .keep objects' '
 	# build on $objsha1, $packsha1, and .keep state from previous
-	git repack -Adl --pack-kept-objects &&
+	git repack -Adl &&
 	test_when_finished "found_duplicate_object=" &&
 	for p in .git/objects/pack/*.idx; do
 		idx=$(basename $p)