Re: [PATCH] change the unpack limit treshold to a saner value

From: Linus Torvalds <torvalds@osdl.org>
Date: Dec 7, 2006, 01:08 UTC
Message-ID: <Pine.LNX.4.64.0612061700120.3542@woody.osdl.org>
In-Reply-To: <Pine.LNX.4.64.0612061420410.2630@xanadu.home>

On Wed, 6 Dec 2006, Nicolas Pitre wrote:

> 
> This is why I think the current default treshold should be 3 instead of 
> the insane value of 5000.  But since it feels a bit odd to go from 5000 
> to 3 I setled on 10.

Definitely not.

We have a much easier time handling many loose packed objects than many pack-files. For many reasons, but two really obvious ones:

 - pack-file indexes get read in on startup, and we maintain an explicit 
   list of them. Having lots of pack-files adds overhead that doesn't 
   exist for lots of loose objects.

 - loose files are spread out over 256 subdirectories to make lookup 
   easier, packfiles are not (and always create an index file too).

So in general, as a trivial heuristic, you probably want about 512 times as many loose objects as you want pack-files, i fonly because of the latter issue, because you can much more easily handle lots of loose objects than lots of pack-files. So it's _not_ a factor of 3. Or even 10.

But since there _is_ reason to do pack-files too, and since using too big a value means that you never end up keeping a pack-file _at_all_ if you pull often, I'd suggest that rather than use a limit of 512 you go for something like 100-200 objects as the threshold (of course, the proper one would depend on the distribution of the size of your pack-files, but I'll just hand-wave and say that together with occasional re-packing, something in that range is _generally_ going to be a good idea).