Re: Handling large files with GIT

On Sun, 12 Feb 2006, Linus Torvalds wrote:

Btw, one thing to realize is that git is inherently a lot better at handling lots of files in _subdirectories_, especially if those subdirectories don't change.

I've never used maildir layout, but if it is a couple of large _flat_ subdirectories, git will potentially handle that a lot worse than if you have a hierarchy of directories.

I say "potentially", because if the directories are all mutable and change, then the flat approach is better. But if they tend to have some kind of stability, a lot of git operations (diffing and merging in particular) are able to see that two subdirectories are 100% equal, and will entirely skip them.

This is a large part of why git performs well on the kernel. Most merges don't actually touch all - or even a very big percentage - of the over thousand subdirectories in the kernel. Git can quickly see and ignore the whole subdirectory when that happens - the SHA1 is exactly the same, so git knows that every file under that subdirectory (and every recursive directory) is the same.

In contrast, if you have a million files in one directory, and 10 of them changed, git will still have to check the SHA1's for matches for the other 999,990 files. Which is going to be slow.

That said, I suspect there's space for optimization. 

		Linus