On Thu, 10 Jan 2008, Linus Torvalds wrote:

quoted text
> 
> 
> On Thu, 10 Jan 2008, Nicolas Pitre wrote:
> > 
> > Here's my rather surprising results:
> > 
> > My kernel repo pack size without the patch:	184275401 bytes
> > Same repo with the above patch applied:		205204930 bytes
> > 
> > So it is only 11% larger.  I was expecting much more.
> 
> It's probably worth doing those statistics on some other projects.
> 
> Maybe the difference to other repositories isn't huge, and maybe the 
> kernel *is* a good test-case, but I just wouldn't take that for granted. 

Obviously.

This was a really crud test, and my initial goal was to quickly dismiss 
Pierre's assertion.  Turns out that he wasn't that wrong after all, and 
if a significant increase in access speed by avoiding zlib for 82% of 
object accesses can also be demonstrated for the kernel, then we have an 
opportunity for some optimization tradeoff with no backward 
compatibility concerns.

quoted text
> Yes, delta's are bound to compress much less well than non-deltas, and 
> especially for tree objects (which is a large chunk of them) they probably 
> compress even less (because a big part of the delta is actually just the 
> SHA1 changes), but if it's 11% on the kernel, it could easily be 25% on 
> something else.

Right.  But again this is not worth pursuing if a significant speed 
increase in repo access is not demonstrated at least with the kernel.


Nicolas
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