Subject: Re: [RFH] git cherry vs. git rev-list --cherry, or: Why does "..." suck?

From: Michael J Gruber <[email-masked]>
Date: Wed, 23 Mar 2011 17:46:05 +0100

Adding some recent insight:

Michael J Gruber venit, vidit, dixit 22.03.2011 13:07:
> Performance
> ===========
> 
> I don't get this:
> 
> git cherry A B: 0.4s
> git rev-list --cherry A...B: 1.7s
> (more details below)

I can get the latter down to 0.95s and this

> merge-base A B: 0.95s
> merge-base --all A B: 0.95s
> rev-parse A...B: 0.95s

to 0.16s each. The downside is that merge-base may give a few
unneccessary candidates (commits which are ancestors of other commits it
returns), but this does not change the results for rev-list, of course.

I get this dramatic speedup by removing the check for duplicates from
get_merge_bases_many() in commit.c. After a first merge_bases_many()
run, returning N commits, that check calls merge_bases_many() again for
each pair (N choose 2) to check whether one is contained in the other.
Quite a bottleneck. Removing it works great. But can we live with a few
additional merge bases?

Michael