On 10/13/2016 01:01 AM, Jeff King wrote:
On Thu, Oct 13, 2016 at 12:30:52AM +0200, Vegard Nossum wrote:
However, the commit found by 'git blame' above appears just fine to me,
I haven't been able to spot a bug in it.
A closer inspection reveals the problem to really be that this is an
extremely hot path with more than -- holy cow -- 4,106,756,451
iterations on the 'packed_git' list for a single 'git fetch' on my
repository. I'm guessing the patch above just made the inner loop
ever so slightly slower.
My .git/objects/pack/ has ~2088 files (1042 idx files, 1042 pack files,
and 4 tmp_pack_* files).
Yeah. I agree that the commit you found makes the check a little more
expensive, but I think the root of the problem is calling
prepare_packed_git_one many times. This _should_ happen once for each
pack at program startup, and possibly again if we need to re-scan the
pack directory to account for racing with a simultaneous repack.
The latter is generally triggered when we fail to look up an object we
expect to exist. So I'd suspect 45e8a74 (has_sha1_file: re-check pack
directory before giving up, 2013-08-30) is playing a part. We dealt with
that to some degree in 0eeb077 (index-pack: avoid excessive re-reading
of pack directory, 2015-06-09), but it would not surprise me if there is
another spot that needs similar treatment.
Does the patch below help?
Yes, ~2m10s -> ~1m25s when I test a git fetch this morning (the other
variation in time may be due to different CPU usage by other programs,
but I ran with/without the patch multiple times and the difference is
consistent).
Thanks,
Vegard