On Sat, Apr 04, 2015 at 09:06:11PM -0400, Jeff King wrote:
> As I've mentioned before, I have some repositories with rather large
> numbers of refs. The worst one has ~13 million refs, for a 1.6GB
> packed-refs file. So I was saddened by this:
>
> $ time git.v2.0.0 rev-parse refs/heads/foo >/dev/null 2>&1
> real 0m6.840s
> user 0m6.404s
> sys 0m0.440s
>
> $ time git.v2.4.0-rc1 rev-parse refs/heads/foo >/dev/null 2>&1
> real 0m19.432s
> user 0m18.996s
> sys 0m0.456s
Here's a re-roll incorporating feedback from the list. Thanks everybody
for your comments. Last time the final number was ~8.5s, which was
disappointingly slower than v2.0.0. In this iteration, my final numbers
are:
real 0m5.703s
user 0m5.276s
sys 0m0.432s
which is quite pleasing.
The big changes that resulted in this additional speedup are:
1. Use getdelim() when it is available. This is much faster than even
a getc_unlocked() loop.
2. The slowdown from d0f810f was from adding in refname_is_safe calls.
But what I didn't notice before is that we run them in _addition_
to check_refname_format, rather than instead of it. So in the
common case of a sanely-formatted refname, we can skip the call,
rather than writing a lot of code to micro-optimize it.
It was also mentioned in a nearby thread that the config code could
benefit from some of the same micro-optimizations. It can't make use of
getdelim(), as it really does want to do character-by-character parsing.
But it can still use getc_unlocked() and the strbuf_avail() trick, which
speeds up config reading by 47%. Those patches are included here.
[1/9]: strbuf_getwholeline: use getc macro
[2/9]: git-compat-util: add fallbacks for unlocked stdio
[3/9]: strbuf_getwholeline: use getc_unlocked
[4/9]: config: use getc_unlocked when reading from file
[5/9]: strbuf_addch: avoid calling strbuf_grow
[6/9]: strbuf_getwholeline: avoid calling strbuf_grow
[7/9]: strbuf_getwholeline: use getdelim if it is available
[8/9]: read_packed_refs: avoid double-checking sane refs
[9/9]: t1430: add another refs-escape test
-Peff
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