On Mon, Oct 29, 2018 at 09:48:02AM +0900, Junio C Hamano wrote: > > Of course any cache raises questions of cache invalidation, but I think > > we've already dealt with that for this case. When we use > > OBJECT_INFO_QUICK, that is a sign that we want to make this kind of > > accuracy/speed tradeoff (which does a similar caching thing with > > packfiles). > > > > So putting that all together, could we have something like: > > I think this conceptually is a vast improvement relative to > ".cloning" optimization. Obviously this does not have the huge > downside of the other approach that turns the collision detection > completely off. > > A real question is how much performance gain, relative to ".cloning" > thing, this approach gives us. If it gives us 80% or more of the > gain compared to doing no checking, I'd say we have a clear winner.
My test runs showed it improving index-pack by about 3%, versus 4% for no collision checking at all. But there was easily 1% of noise. And much more importantly, that was on a Linux system on ext4, where stat is fast. I'd be much more curious to hear timing results from people on macOS or Windows, or from Geert's original NFS case. -Peff
