Re: Some git performance measurements..

From: Junio C Hamano <gitster@pobox.com>
Date: Nov 29, 2007, 05:17 UTC
Message-ID: <7vr6i9y6ju.fsf@gitster.siamese.dyndns.org>
In-Reply-To: <alpine.LFD.0.9999.0711281747450.8458@woody.linux-foundation.org>

Linus Torvalds <torvalds@linux-foundation.org> writes:

> Less than a hundredth of a second may not sound much, but when we have 
> 1700+ directories in the kernel trees, doing that for each possible 
> .gitignore file is really really expensive!

The only thing that wants to use excluded() in the unpack_trees() codepath is the code to allow overwriting an existing, untracked file in verify_absent(). When we find an untracked file at the same path as we are just trying to check out a file, we allow overwriting it only if that file is "ignored".

But the way the unpack_trees_rec() and the gitignore handling in dir.c are structured currently means we do push/pop exclude-per-directory stack as we enter and leave a new subdirectory. We do not do this lazily on demand.

The newer gitattributes subsystem maintains a similar per-directory data structure but this is purely done on-demand; until somebody asks "what are the attrs for this path", we do not read .gitattributes file. We should be able to restructure exclude-per-directory code in a similar way.