From: Brandon Williams <bmwill@google.com>
Date: Wed, 04 Apr 2018 17:01:31 GMT
Subject: Re: [PATCH 8/6] commit: use generation numbers for in_merge_bases()
Message-ID: <20180404170131.GD100220@google.com>
In-Reply-To: <14e4e1d3-5c77-dc7c-10d5-e9406b992f0e@gmail.com>

On 04/04, Derrick Stolee wrote:
> On 4/4/2018 11:45 AM, Derrick Stolee wrote:
> > The containment algorithm for 'git branch --contains' is different
> > from that for 'git tag --contains' in that it uses is_descendant_of()
> > instead of contains_tag_algo(). The expensive portion of the branch
> > algorithm is computing merge bases.
> > 
> > When a commit-graph file exists with generation numbers computed,
> > we can avoid this merge-base calculation when the target commit has
> > a larger generation number than the target commits.
> > 
> > Performance tests were run on a copy of the Linux repository where
> > HEAD is contained in v4.13 but no earlier tag. Also, all tags were
> > copied to branches and 'git branch --contains' was tested:
> > 
> > Before: 60.0s
> > After:   0.4s
> > Rel %: -99.3%

Now that is an impressive speedup.

-- 
Brandon Williams