[PATCH 2/3] repack: add --keep-unreachable option
- From
Jeff King <peff@peff.net>
- Date
- Jun 13, 2016, 04:36 UTC
- Message-ID
- <20160613043628.GB3902@sigill.intra.peff.net>
- In-Reply-To
- <20160613043313.GA29422@sigill.intra.peff.net>
The usual way to do a full repack (and what is done by git-gc) is to run "repack -Ad --unpack-unreachable=<when>", which will loosen any unreachable objects newer than "<when>", and drop any older ones.
This is a safer alternative to "repack -ad", because "<when>" becomes a grace period during which we will not drop any new objects that are about to be referenced. However, it isn't perfectly safe. It's always possible that a process is about to reference an old object. Even if that process were to take care to update the timestamp on the object, there is no atomicity with a simultaneously running "repack" process.
So while unlikely, there is a small race wherein we may drop an object that is in the process of being referenced. If you do automated repacking on a large number of active repositories, you may hit it eventually, and the result is a corrupted repository.
It would be nice to fix that race in the long run, but it's complicated. In the meantime, there is a much simpler strategy for automated repository maintenance: do not drop objects at all. We already have a "--keep-unreachable" option in pack-objects; we just need to plumb it through from git-repack.
Note that this _isn't_ plumbed through from git-gc, so at this point it's strictly a tool for people doing their own advanced repository maintenance strategy.
Signed-off-by: Jeff King <peff@peff.net> --- Documentation/git-repack.txt | 6 ++++++ builtin/repack.c | 9 +++++++++ t/t7701-repack-unpack-unreachable.sh | 15 +++++++++++++++ 3 files changed, 30 insertions(+)
diff --git a/Documentation/git-repack.txt b/Documentation/git-repack.txt index cde7b44..68702ea 100644 --- a/Documentation/git-repack.txt +++ b/Documentation/git-repack.txt @@ -134,6 +134,12 @@ other objects in that pack they already have locally. the write of any objects that would be immediately pruned by a follow-up `git prune`. +-k:: +--keep-unreachable:: + When used with `-ad`, any unreachable objects from existing + packs will be appended to the end of the packfile instead of + being removed. + Configuration ------------- diff --git a/builtin/repack.c b/builtin/repack.c index 858db38..573e66c 100644 --- a/builtin/repack.c +++ b/builtin/repack.c @@ -146,6 +146,7 @@ int cmd_repack(int argc, const char **argv, const char *prefix) int pack_everything = 0; int delete_redundant = 0; const char *unpack_unreachable = NULL; + int keep_unreachable = 0; const char *window = NULL, *window_memory = NULL; const char *depth = NULL; const char *max_pack_size = NULL; @@ -175,6 +176,8 @@ int cmd_repack(int argc, const char **argv, const char *prefix) N_("write bitmap index")), OPT_STRING(0, "unpack-unreachable", &unpack_unreachable, N_("approxidate"), N_("with -A, do not loosen objects older than this")), + OPT_BOOL('k', "keep-unreachable", &keep_unreachable, + N_("with -a, repack unreachable objects")), OPT_STRING(0, "window", &window, N_("n"), N_("size of the window used for delta compression")), OPT_STRING(0, "window-memory", &window_memory, N_("bytes"), @@ -196,6 +199,10 @@ int cmd_repack(int argc, const char **argv, const char *prefix) if (delete_redundant && repository_format_precious_objects) die(_("cannot delete packs in a precious-objects repo")); + if (keep_unreachable && + (unpack_unreachable || (pack_everything & LOOSEN_UNREACHABLE))) + die(_("--keep-unreachable and -A are incompatible")); + if (pack_kept_objects < 0) pack_kept_objects = write_bitmaps; @@ -239,6 +246,8 @@ int cmd_repack(int argc, const char **argv, const char *prefix) } else if (pack_everything & LOOSEN_UNREACHABLE) { argv_array_push(&cmd.args, "--unpack-unreachable"); + } else if (keep_unreachable) { + argv_array_push(&cmd.args, "--keep-unreachable"); } else { argv_array_push(&cmd.env_array, "GIT_REF_PARANOIA=1"); } diff --git a/t/t7701-repack-unpack-unreachable.sh b/t/t7701-repack-unpack-unreachable.sh index b66e383..f13df43 100755 --- a/t/t7701-repack-unpack-unreachable.sh +++ b/t/t7701-repack-unpack-unreachable.sh @@ -122,4 +122,19 @@ test_expect_success 'keep packed objects found only in index' ' git cat-file blob :file ' +test_expect_success 'repack -k keeps unreachable packed objects' ' + # create packed-but-unreachable object + sha1=$(echo unreachable-packed | git hash-object -w --stdin) && + pack=$(echo $sha1 | git pack-objects .git/objects/pack/pack) && + git prune-packed && + + # -k should keep it + git repack -adk && + git cat-file -p $sha1 && + + # and double check that without -k it would have been removed + git repack -ad && + test_must_fail git cat-file -p $sha1 +' + test_done
-- 2.9.0.rc2.149.gd580ccd