Re: [PATCH] commit: detect commits that exist in commit-graph but not in the ODB

From: Junio C Hamano <gitster@pobox.com>
Date: Oct 17, 2023, 18:34 UTC
Message-ID: <xmqqjzrlhzci.fsf@gitster.g>
In-Reply-To: <ZS4rmtBTYnp2RMiY@tanuki>

Patrick Steinhardt <ps@pks.im> writes:

Show 9 quoted lines

> Fair point indeed. The following is a worst-case scenario benchmark of
> of the change where we do a full topological walk of all reachable
> commits in the graph, executed in linux.git. We parse commit parents via
> `repo_parse_commit_gently()`, so the new code path now basically has to
> check for object existence of every reachable commit:
> ...
> The added check does lead to a performance regression indeed, which is
> not all that unexpected. That being said, the commit-graph still results
> in a significant speedup compared to the case where we don't have it.

Yeah, I agree that both points are expected. An extra check that is much cheaper than the full parsing is paying a small price to be a bit more careful than before. The question is if the price is small enough. I am still not sure if the extra carefulness is warranted for all normal cases to spend 30% extra cycles

Thanks.