Subject: Re: git gc --aggressive led to about 40 times slower "git log --raw"

From: Junio C Hamano <[email-masked]>
Date: Fri, 21 Feb 2014 09:36:14 -0800

Christian Jaeger <[email-masked]> writes:

> Also, in "man git-gc" document --aggressive that it leads to slower
> *read* performance after the gc, I remember having red that option's
> docs when I ran it, and since it didn't mention that it makes reads
> slower, I didn't expect it to, and thus didn't remember this as the
> source of the problem when I noticed that things were slow.

Good point. We would at least need such a documentation update to
warn users.

> (But, I took from the discussion that increasing the gzip window size
> (?) would make things smaller anyway, so perhaps all that isn't even
> necessary?)

If you are talking about "--window" in "git repack --window=xxxx",
that is not related to gzip.  It is how many other "similar" objects
an object will be tried to delta against to find a smallest delta
that can represent it in the pack.  Such a better delta, if found,
can give you a packfile with a smaller depth that is as small as
another packfile created with a larger depth, which is an overall
win, and using a wider window is a way to achieve such a result.