Re: commit-graph is cool (overcoming add_missing_tags() perf issues)

> Hi,
>
> Just wanted to give a shout-out for the commit-graph work and how
> impressive it is.  I had an internal report from a user that git
> pushes containing only one new tiny commit were taking over a minute
> (in a moderate size repo with good network connectivity). After
> digging for a while, I noticed three unusual things about the repo[1]:
>    * he had push.followTags set to true
>    * upstream repo had about 20k tags (despite only 55k commits)
>    * his repo had an additional 2.5k tags, but none of these were in
>      the history of the branches he was pushing and thus would not be
>      included in any pushes.
>
> Digging in, almost all the time was CPU-bound and spent in
> add_missing_tags()[2].  If I'm reading the code correctly, it appears
> that function loops over each tag, calling in_merge_bases_many() once
> per tag.  Thus, for his case, we were potentially walking all of
> history of the main branch 2.5k times.  That seemed rather suboptimal.