Re: pack operation is thrashing my server

From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Aug 14, 2008, 17:21 UTC
Message-ID: <alpine.LFD.1.10.0808141014410.3324@nehalem.linux-foundation.org>
In-Reply-To: <alpine.LFD.1.10.0808131228270.4352@xanadu.home>

On Wed, 13 Aug 2008, Nicolas Pitre wrote:

Show 12 quoted lines

> 
> A much better solution would consist of finding just _why_ object 
> enumeration is so slow.  This is indeed my biggest grip with git 
> performance at the moment.
> 
> |nico@xanadu:linux-2.6> time git rev-list --objects --all > /dev/null
> |
> |real    0m21.742s
> |user    0m21.379s
> |sys     0m0.360s
> 
> That's way too long for 1030198 objects (roughly 48k objects/sec).

Why do you think that's horribly slow?

Doing a rev-list of all objects is a fairly rare operation, but even if you want to clone/repack all of your archives the whole time, please realize that listing objects is _not_ a simple operation. It opens up and parses every single tree in the whole history. That's a _lot_ of data to unpack.

And trees also pack very efficiently (because they delta so well), so there's a lot of complex ops there.

> And it gets even worse with the gcc repository:

I bet it's because gcc has a different directory structure. I don't have the gcc sources in front of me, but I'd suspect something like a single large directory or other.

> Clearly something is not scaling here.

I don't agree. There's no "clearly" about it. Different data sets.

		Linus