Re: [PATCH V1][RFC] t/perf/p3400: speed up setup using fast-import

From: Tian Yuchen <a3205153416@gmail.com>
Date: Jan 28, 2026, 04:33 UTC
Message-ID: <CA+rU_o7dZB=OCJHk9nGSbs4RLXmE9A3VUopa+6vF6oX0E9vxuQ@mail.gmail.com>
In-Reply-To: <CA+rU_o5pzpHvvo=PwMV1-JUUa37Qp=B+-X3QqeXh-VRdNdA9DA@mail.gmail.com>

Tian Yuchen <a3205153416@gmail.com> writes：

Show 15 quoted lines

>
> I noticed that while the setup phase is much faster (as shown in the commit
> message), the actual rebase performance test regressed slightly by about 3
> seconds (from ~2s to ~5s). I don't quite understand what led to this outcome.
>
> Additionally, I haven't delved deeply into the technical details of
> `git fast-import`,
> and I'm not entirely sure if my approach is reasonable and compliant with the
> specifications.
>
> I would greatly appreciate any guidance from those knowledgeable in these
> area!
>
> Regards,
> Yuchen

I highly suspect that git fast-import generate the packfile that is NOT delta compressed. According to git fast-import documentation:

>...For this reason it is strongly recommended that users repack the repository with
>'git repack -a -d' after fast-import completes, allowing Git to reorganize the packfiles
>for faster data access...

Could this be the reason why it's even slower than handling “loose objects”? I'm working on it currently.

Regards, Yuchen