From: Junio C Hamano <gitster@pobox.com>
Date: Fri, 08 Aug 2008 22:59:16 GMT
Subject: Re: [PATCH] git-svn: Make it scream by minimizing temp files
Message-ID: <7vd4kjazaz.fsf@gitster.siamese.dyndns.org>
In-Reply-To: <1218235313-19480-1-git-send-email-marcus@griep.us>

Marcus Griep <marcus@griep.us> writes:

> Currently, git-svn would create a temp file on four occasions:
> 1. Reading a blob out of the object db
> 2. Creating a delta from svn
> 3. Hashing and writing a blob into the object db
> 4. Reading a blob out of the object db (in another place in code)
>
> Any time git-svn did the above, it would dutifully create and then
> delete said temp file.  Unfortunately, this means that between 2-4
> temporary files are created/deleted per file 'add/modify'-ed in
> svn (O(n)).  This causes significant overhead and helps the inode
> counter to spin beautifully.
>
> By its nature, git-svn is a serial beast.  Thus, reusing a temp file
> does not pose significant problems.  "truncate and seek" takes much
> less time than "unlink and create".  This patch centralizes the
> tempfile creation and holds onto the tempfile until they are deleted
> on exit.  This significantly reduces file overhead, now requiring
> at most three (3) temp files per run (O(1)).

Beautifully written analysis of the issue being tackled.

But optimization patch should be backed by numbers --- do you have a
benchmark result of some sort that you would want to include here?