Re: [PATCH 4/4] gc --aggressive: three phase repacking

From: Duy Nguyen <pclouds@gmail.com>
Date: Mar 18, 2014, 05:00 UTC
Message-ID: <CACsJy8CU3JyL74OuurjDr5-FHmBOCRahtXukukCqGx1cTdjvMQ@mail.gmail.com>
In-Reply-To: <20140318045050.GB8240@sigill.intra.peff.net>

On Tue, Mar 18, 2014 at 11:50 AM, Jeff King <peff@peff.net> wrote:

Show 13 quoted lines

> On Sun, Mar 16, 2014 at 08:35:04PM +0700, Nguyễn Thái Ngọc Duy wrote:
>
>> As explained in the previous commit, current aggressive settings
>> --depth=250 --window=250 could slow down repository access
>> significantly. Notice that people usually work on recent history only,
>> we could keep recent history more loosely packed, so that repo access
>> is fast most of the time while the pack file remains small.
>
> One thing I have not seen is real-world timings showing the slowdown
> based on --depth. Did I miss them, or are we just making assumptions
> based on one old case from 2009 (that, AFAIK does not have real numbers,
> just speculation)? Has anyone measured the effect of bumping the delta
> cache size (and its hash implementation)?

David tested it with git-blame [1]. I should probably run some tests too (I don't remember if I tested some operations last time).

http://thread.gmane.org/gmane.comp.version-control.git/242277/focus=242435

Show 11 quoted lines

>> git.git is not a great repo to test it because its size is modest but
>> so are my laptop's cpu and memory, so here are the timings and pack
>> sizes
>>
>>             size  time
>> old aggr.   36MB  5m51
>> new aggr.   37MB  6m13
>> repack -adf 48MB  1m12
>
> I am not clear on what these times mean. It looks like the new code is
> slower _and_ bigger. Can you explain them?

That's right :) The upside is faster operations, which is complely missed here. The good thing from those numbers is pack size does not increase much (the upper limit would be repack -adf with default settings).

-- 
Duy