From: Jeff King <peff@peff.net>
Date: Sat, 21 Mar 2020 05:04:55 GMT
Subject: Re: [PATCH 0/1] commit-graph: avoid unnecessary tag deference when merging
Message-ID: <20200321050455.GB1438317@coredump.intra.peff.net>
In-Reply-To: <xmqqo8sq9uhb.fsf@gitster.c.googlers.com>

On Fri, Mar 20, 2020 at 09:56:16PM -0700, Junio C Hamano wrote:

> Taylor Blau <me@ttaylorr.com> writes:
> 
> > This patch avoids an unnecessary tag dereference in
> > 'merge_commit_graph()', which can improve the running time of a
> > commit-graph write by around ~7.4% on average.
> 
> That I suspect depends heavily on what portion of your total
> committishes consist of tags, no (in an absurdly extreme case, if
> there is no tag in the repository, there won't be any improvement)?
> 
> What tag-vs-commit ratio is the above "average" number based on?

I think the point is that in this code path we've already identified the
candidates as commits (because they were in an existing commit-graph
file), so treating the items as a committishes in the first place is
unnecessary. If an object isn't itself a commit, we should be dropping
it from the proposed output (possibly we ought to give a warning in such
a case, too, as it indicates the previous writer did something wrong).

-Peff