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

From: Junio C Hamano <gitster@pobox.com>
Date: Feb 21, 2014, 17:36 UTC
Message-ID: <xmqq4n3s5pwx.fsf@gitster.dls.corp.google.com>
In-Reply-To: <CAEjYwfU7un6wuA0Z-hSycROSWNdfQq1NawC7=+cNZeNu4-DpJg@mail.gmail.com>

Christian Jaeger <chrjae@gmail.com> writes:

Show 5 quoted lines

> 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.