repack: add `repack.packKeptObjects` config var

The git-repack command always passes `--honor-pack-keep`
to pack-objects. This has traditionally been a good thing,
as we do not want to duplicate those objects in a new pack,
and we are not going to delete the old pack.

However, when bitmaps are in use, it is important for a full
repack to include all reachable objects, even if they may be
duplicated in a .keep pack. Otherwise, we cannot generate
the bitmaps, as the on-disk format requires the set of
objects in the pack to be fully closed.

Even if the repository does not generally have .keep files,
a simultaneous push could cause a race condition in which a
.keep file exists at the moment of a repack. The repack may
try to include those objects in one of two situations:

  1. The pushed .keep pack contains objects that were
     already in the repository (e.g., blobs due to a revert of
     an old commit).

  2. Receive-pack updates the refs, making the objects
     reachable, but before it removes the .keep file, the
     repack runs.

In either case, we may prefer to duplicate some objects in
the new, full pack, and let the next repack (after the .keep
file is cleaned up) take care of removing them.

This patch introduces both a command-line and config option
to disable the `--honor-pack-keep` option.  By default, it
is triggered when pack.writeBitmaps (or `--write-bitmap-index`
is turned on), but specifying it explicitly can override the
behavior (e.g., in cases where you prefer .keep files to
bitmaps, but only when they are present).

Note that this option just disables the pack-objects
behavior. We still leave packs with a .keep in place, as we
do not necessarily know that we have duplicated all of their
objects.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 12 insertions, 1 deletions

diff --git a/builtin/repack.c b/builtin/repack.c
index 239f278fac..50cc281527 100644
--- a/builtin/repack.c
+++ b/builtin/repack.c
@@ -9,6 +9,7 @@
 #include "argv-array.h"
 
 static int delta_base_offset = 1;
+static int pack_kept_objects = -1;
 static char *packdir, *packtmp;
 
 static const char *const git_repack_usage[] = {
@@ -22,6 +23,10 @@ static int repack_config(const char *var, const char *value, void *cb)
 		delta_base_offset = git_config_bool(var, value);
 		return 0;
 	}
+	if (!strcmp(var, "repack.packkeptobjects")) {
+		pack_kept_objects = git_config_bool(var, value);
+		return 0;
+	}
 	return git_default_config(var, value, cb);
 }
 
@@ -175,6 +180,8 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 				N_("limits the maximum delta depth")),
 		OPT_INTEGER(0, "max-pack-size", &max_pack_size,
 				N_("maximum size of each packfile")),
+		OPT_BOOL(0, "pack-kept-objects", &pack_kept_objects,
+				N_("repack objects in packs marked with .keep")),
 		OPT_END()
 	};
 
@@ -183,6 +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());
 
@@ -190,7 +200,8 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 
 	argv_array_push(&cmd_args, "pack-objects");
 	argv_array_push(&cmd_args, "--keep-true-parents");
-	argv_array_push(&cmd_args, "--honor-pack-keep");
+	if (!pack_kept_objects)
+		argv_array_push(&cmd_args, "--honor-pack-keep");
 	argv_array_push(&cmd_args, "--non-empty");
 	argv_array_push(&cmd_args, "--all");
 	argv_array_push(&cmd_args, "--reflog");