On Mon, Oct 29, 2018 at 09:34:53PM +0000, Geert Jansen wrote: > As an example, this means that when you're recieving a pack file with 1K > objects in a repository with 10K loose objects that the loose-object-cache > patch has roughly the same performance as the current git. I'm not sure if > this > is something to worry about as I'm not sure people run repos with this many > loose files. If it is a concern, there could be a flag to turn the loose > object > cache on/off.
So yeah, that's the other thing I'm thinking about regarding having a maximum loose cache size. 10k objects is only 200KB in memory. That's basically nothing. At some point you run into pathological cases, like having a million objects (but that's still only 20MB, much less than we devote to other caches, though of course they do add up). If you have a million loose objects, I strongly suspect you're going to run into other problems (like space, since you're not getting any deltas). The one thing that gives me pause is that if you have a bunch of unused and unreachable loose objects on disk, most operations won't actually look at them at all. The majority of operations are only looking for objects we expect to be present (e.g., resolving a ref, walking a tree) and are fulfilled by checking the pack indices first. So it's possible that Git is _tolerable_ for most operations with a million loose objects, and we could make it slightly worse by loading the cache. But I find it hard to get too worked up about spending an extra 20MB (and the time to readdir() it in) in that case. It seems like about 400ms on my machine, and the correct next step is almost always going to be "pack" or "prune" anyway. -Peff
