Re: [PATCH] packfile: fix perf regression with many packs

[Patrick Steinhardt <ps@pks.im>]

On Thu, Aug 13, 2026 at 12:15:25PM -0400, Jeff King wrote:
> On Thu, Aug 13, 2026 at 09:35:49AM +0200, Patrick Steinhardt wrote:
> 
> > An alternative would be to use a hashmap here that tracks the packs that
> > have already been added. It has the advantage that it also covers the
> > `prepend()` operation and that callers don't have to be aware of this
> > mechanism at all. Furthermore, moving preexisting entries to the back or
> > front could become O(logn) if the list was doubly-linked. We do this
> > operation quite often to re-sort entries in the list when looking up
> > objects.
> 
> Don't we already use such a hashmap via packfile_store_add_pack() and
> packfile_store_load_pack()? That comes from ec48540fe8 (packfile.c:
> speed up loading lots of packfiles, 2019-11-27) and is how we know that
> this "is_new" flag is true (otherwise we'd get duplicates during
> "reprepare" operations).

That's a good point, we indeed do! Maybe it would make sense then to
remove that map from the packfile store and instead move it into the
packfile list to make it more generally useful.

Patrick