repack: add --keep-unreachable option
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> Signed-off-by: Junio C Hamano <gitster@pobox.com>
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@ -134,6 +134,12 @@ other objects in that pack they already have locally.
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the write of any objects that would be immediately pruned by
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a follow-up `git prune`.
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-k::
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--keep-unreachable::
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When used with `-ad`, any unreachable objects from existing
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packs will be appended to the end of the packfile instead of
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being removed.
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Configuration
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-------------
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@ -146,6 +146,7 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
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int pack_everything = 0;
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int delete_redundant = 0;
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const char *unpack_unreachable = NULL;
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int keep_unreachable = 0;
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const char *window = NULL, *window_memory = NULL;
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const char *depth = NULL;
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const char *max_pack_size = NULL;
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@ -175,6 +176,8 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
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N_("write bitmap index")),
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OPT_STRING(0, "unpack-unreachable", &unpack_unreachable, N_("approxidate"),
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N_("with -A, do not loosen objects older than this")),
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OPT_BOOL('k', "keep-unreachable", &keep_unreachable,
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N_("with -a, repack unreachable objects")),
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OPT_STRING(0, "window", &window, N_("n"),
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N_("size of the window used for delta compression")),
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OPT_STRING(0, "window-memory", &window_memory, N_("bytes"),
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@ -196,6 +199,10 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
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if (delete_redundant && repository_format_precious_objects)
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die(_("cannot delete packs in a precious-objects repo"));
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if (keep_unreachable &&
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(unpack_unreachable || (pack_everything & LOOSEN_UNREACHABLE)))
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die(_("--keep-unreachable and -A are incompatible"));
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if (pack_kept_objects < 0)
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pack_kept_objects = write_bitmaps;
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@ -239,6 +246,8 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
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} else if (pack_everything & LOOSEN_UNREACHABLE) {
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argv_array_push(&cmd.args,
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"--unpack-unreachable");
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} else if (keep_unreachable) {
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argv_array_push(&cmd.args, "--keep-unreachable");
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} else {
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argv_array_push(&cmd.env_array, "GIT_REF_PARANOIA=1");
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}
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@ -122,4 +122,19 @@ test_expect_success 'keep packed objects found only in index' '
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git cat-file blob :file
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'
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test_expect_success 'repack -k keeps unreachable packed objects' '
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# create packed-but-unreachable object
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sha1=$(echo unreachable-packed | git hash-object -w --stdin) &&
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pack=$(echo $sha1 | git pack-objects .git/objects/pack/pack) &&
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git prune-packed &&
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# -k should keep it
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git repack -adk &&
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git cat-file -p $sha1 &&
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# and double check that without -k it would have been removed
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git repack -ad &&
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test_must_fail git cat-file -p $sha1
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'
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test_done
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