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

[Jeff King <peff@peff.net>]

On Tue, Mar 18, 2014 at 12:00:48PM +0700, Duy Nguyen wrote:

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

Ah, thanks. I do remember that thread now.

It looks like David's last word is that he gets a significant
performance from bumping the delta base cache size (and number of
buckets). And that matches the timings I just did. I suspect there are
still pathological cases that could behave worse, but it really sounds
like we should be looking into improving that cache as a first step.

-Peff