Re: [PATCH] write-tree performance problems

On Tue, 19 Apr 2005, Chris Mason wrote:

Note that I don't think you want to replace quilt with git. The approaches are totally different, and git does _not_ obviate the need for the quilt kind of "patch testing".

In fact, git has all the same issues that BK had, and for the same fundamental reason: if you do distributed work, you have to always "append" stuff, and that means that you can never re-order anything after the fact.

So git really is _not_ very good at all at doing what quilt does. Also, there's an inevitable cost of being careful, and as you note, the sha1 calculation is expensive (*).

However, I hate your modification. Yeah, I know, performance is important to me, but even more than performance is that I can trust the end results, and that means that we calculate the hashes instead of just taking them from somewhere else..

What I _would_ like is the ability to re-use an old tree, though. What you really want to do is not pass in a set of directory names and just trust that they are correct, but just pass in a directory to compare with, and if the contents match, you don't need to write out a new one.

I'll try to whip up something that does what you want done, but doesn't need (or take) any untrusted information from the user in the form "trust me, it hasn't changed".

		Linus

(*) Actually, I think it's the compression that ends up being the most expensive part.