Colin Stolley [off-list ref] wrote:

When loading packfiles on start-up, we traverse the internal packfile
list once per file to avoid reloading packfiles that have already
been loaded. This check runs in quadratic time, so for poorly
maintained repos with a large number of packfiles, it can be pretty
slow.

Cool!  Thanks for looking into this, and I've been having
trouble in that department with big alternates files.

Add a hashmap containing the packfile names as we load them so that
the average runtime cost of checking for already-loaded packs becomes
constant.

Btw, would you have time to do a comparison against khash?

AFAIK hashmap predates khash in git; and hashmap was optimized
for removal.   Removals don't seem to be a problem for pack
loading.

I'm interested in exploring the removing of hashmap entirely in
favor of khash to keep our codebase smaller and easier-to-learn.
khash shows up more in other projects, and ought to have better
cache-locality.

Thanks again.