Subject: hashmap vs khash? Re: [PATCH] packfile.c: speed up loading lots of packfiles.

From: Eric Wong <[email-masked]>
Date: Thu, 28 Nov 2019 00:42:02 +0000

Colin Stolley <[email-masked]> 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.