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author | Jeff King <peff@peff.net> | 2016-07-29 00:10:31 -0400 |
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committer | Junio C Hamano <gitster@pobox.com> | 2016-07-29 11:05:07 -0700 |
commit | cd3799679533328dcf262549c9d6466b07628df1 (patch) | |
tree | 73bbcc339b1c141b813e7aae6a2fad8bc9903b59 /Documentation/RelNotes/2.5.2.txt | |
parent | find_pack_entry: replace last_found_pack with MRU cache (diff) | |
download | tgif-cd3799679533328dcf262549c9d6466b07628df1.tar.xz |
pack-objects: break out of want_object loop early
When pack-objects collects the list of objects to pack
(either from stdin, or via its internal rev-list), it
filters each one through want_object_in_pack().
This function loops through each existing packfile, looking
for the object. When we find it, we mark the pack/offset
combo for later use. However, we can't just return "yes, we
want it" at that point. If --honor-pack-keep is in effect,
we must keep looking to find it in _all_ packs, to make sure
none of them has a .keep. Likewise, if --local is in effect,
we must make sure it is not present in any non-local pack.
As a result, the sum effort of these calls is effectively
O(nr_objects * nr_packs). In an ordinary repository, we have
only a handful of packs, and this doesn't make a big
difference. But in pathological cases, it can slow the
counting phase to a crawl.
This patch notices the case that we have neither "--local"
nor "--honor-pack-keep" in effect and breaks out of the loop
early, after finding the first instance. Note that our worst
case is still "objects * packs" (i.e., we might find each
object in the last pack we look in), but in practice we will
often break out early. On an "average" repo, my git.git with
8 packs, this shows a modest 2% (a few dozen milliseconds)
improvement in the counting-objects phase of "git
pack-objects --all <foo" (hackily instrumented by sticking
exit(0) right after list_objects).
But in a much more pathological case, it makes a bigger
difference. I ran the same command on a real-world example
with ~9 million objects across 1300 packs. The counting time
dropped from 413s to 45s, an improvement of about 89%.
Note that this patch won't do anything by itself for a
normal "git gc", as it uses both --honor-pack-keep and
--local.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'Documentation/RelNotes/2.5.2.txt')
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