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From: Junio C Hamano <gitster@pobox.com>
To: Eric Wong <e@80x24.org>
Cc: Colin Stolley <cstolley@runbox.com>, git@vger.kernel.org
Subject: Re: hashmap vs khash? Re: [PATCH] packfile.c: speed up loading lots of packfiles.
Date: Sat, 30 Nov 2019 09:36:47 -0800	[thread overview]
Message-ID: <xmqqeexp2rm8.fsf@gitster-ct.c.googlers.com> (raw)
In-Reply-To: <20191128004202.GA25910@dcvr> (Eric Wong's message of "Thu, 28 Nov 2019 00:42:02 +0000")

Eric Wong <e@80x24.org> writes:

> Colin Stolley <cstolley@runbox.com> 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.

Sounds fun ;-) and useful.

  reply	other threads:[~2019-11-30 17:36 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-27 22:24 [PATCH] packfile.c: speed up loading lots of packfiles Colin Stolley
2019-11-28  0:42 ` hashmap vs khash? " Eric Wong
2019-11-30 17:36   ` Junio C Hamano [this message]
2019-12-02 14:39   ` Jeff King
2019-12-02 17:40 ` SZEDER Gábor
2019-12-02 19:42   ` Jeff King
2019-12-03  6:17     ` Taylor Blau
2019-12-03 15:34       ` Jeff King
2019-12-03 16:04     ` Junio C Hamano
2019-12-03 17:33       ` Colin Stolley
2019-12-03 22:18         ` Jeff King
2019-12-04 18:15           ` Junio C Hamano
2019-12-03 22:17       ` Jeff King
2019-12-04  4:23         ` Jonathan Nieder
2019-12-03  6:19 ` Taylor Blau

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