Subject: Re: [PATCH v2] Bump core.deltaBaseCacheLimit to 128MiB

From: David Kastrup <[email-masked]>
Date: Fri, 21 Mar 2014 07:12:40 +0100

Jeff King <[email-masked]> writes:

> On Wed, Mar 19, 2014 at 01:38:32PM +0100, David Kastrup wrote:
>
>> The default of 16MiB causes serious thrashing for large delta chains
>> combined with large files.
>
> Does it make much sense to bump this without also bumping
> MAX_DELTA_CACHE in sha1_file.c? In my measurements of linux.git, bumping
> the memory limit did not help much without also bumping the number of
> slots.

In the cases I checked, bumping MAX_DELTA_CACHE did not help much.
Bumping it once to 512 could be a slight improvement; larger values then
caused performance to regress.

> I guess that just bumping the memory limit would help with repos which
> have deltas on large-ish files (whereas the kernel just has a lot of
> deltas on a lot of little directories),

Well, those were the most pathological for git-blame so I was somewhat
focused on them.

> but I'd be curious how much.

http://repo.or.cz/r/wortliste.git

consists basically of adding lines to a single alphabetically sorted
file wortliste of currently size 15MB.

-- 
David Kastrup