On Wed, Feb 19, 2014 at 3:38 PM, Philippe Vaucher <philippe.vauc...@gmail.com> wrote: >> fwiw this is the thread that added --depth=250 >> >> http://thread.gmane.org/gmane.comp.gcc.devel/94565/focus=94626 > > This post is quite interesting: > http://article.gmane.org/gmane.comp.gcc.devel/94637
Especially this part -- 8< -- And quite frankly, a delta depth of 250 is likely going to cause overflows in the delta cache (which is only 256 entries in size *and* it's a hash, so it's going to start having hash conflicts long before hitting the 250 depth limit). -- 8< -- So in order to get file A's content, we go through its 250 level chain (and fill the cache), then we get to file B and do the same, which evicts nearly everything from A. By the time we go to the next commit, we have to go through 250 levels for A again because the cache is pretty much useless. I can think of two improvements we could make, either increase cache size dynamically (within limits) or make it configurable. If we have N entries in worktree (both trees and blobs) and depth M, then we might need to cache N*M objects for it to be effective. Christian, if you want to experiment this, update MAX_DELTA_CACHE in sha1_file.c and rebuild. The other is smarter eviction, instead of throwing all A's cached items out (based on recent order), keep the last few items of A and evict B's oldest cached items. Hopefully by the next comit, we can still reuse some cache for A and other files/trees. Delta cache needs to learn about grouping to achieve this. -- Duy -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
