Re: Perf bug: rev-list w/ 2+ paths relatively slow with commit-graph

[Lidong Yan <yldhome2d2@gmail.com>]

Junio C Hamano <gitster@pobox.com> writes：
> 
> Kai Koponen <kaikoponen@google.com> writes:
> 
>> I see, more of a perf FR than a bug then.
>> I don't have much expertise here, but on the surface of it, it doesn't
>> seem to me like there would be any reason the algorithm couldn't check
>> each path's bloom filter in turn while searching, other than that this
>> would be a large and annoying change.
> 
> It looks like that the necessary changes are probably fairly well
> isolated to two functions, i.e., prepare_to_use_bloom_filter() and
> forbid_bloom_filters().  Right now, for a pathspec that has one
> element "dir/file", the code uses two bloom keys for "dir" and
> "dir/file", but if we have "dir1/file1" as well, then it does look
> like a matter of using two more (and the bloom_keys[] array is
> designed to be variable length).

I believe the issue here is that revs->bloom_keys[] represents an
AND condition, whereas what we actually want is an OR. In Kai’s example,
we’re trying to identify commits that modified either src/Make.dist or
src/clean.bash. However, by adding src, Make.dist, and clean.bash to the
bloom_keys, we end up filtering for commits that modified all of these, rather
than any of them.

> But those who have more intimate knowledge in the area than I do may
> point out what is missing in my "it looks like" gut feeling.
>