Jeff King <peff@xxxxxxxx> writes: > On Tue, Mar 18, 2014 at 12:00:48PM +0700, Duy Nguyen wrote: > >> On Tue, Mar 18, 2014 at 11:50 AM, Jeff King <peff@xxxxxxxx> wrote: >> > On Sun, Mar 16, 2014 at 08:35:04PM +0700, Nguyễn Thái Ngọc Duy wrote: >> > >> >> As explained in the previous commit, current aggressive settings >> >> --depth=250 --window=250 could slow down repository access >> >> significantly. Notice that people usually work on recent history only, >> >> we could keep recent history more loosely packed, so that repo access >> >> is fast most of the time while the pack file remains small. >> > >> > One thing I have not seen is real-world timings showing the slowdown >> > based on --depth. Did I miss them, or are we just making assumptions >> > based on one old case from 2009 (that, AFAIK does not have real numbers, >> > just speculation)? Has anyone measured the effect of bumping the delta >> > cache size (and its hash implementation)? >> >> David tested it with git-blame [1]. I should probably run some tests >> too (I don't remember if I tested some operations last time). >> >> http://thread.gmane.org/gmane.comp.version-control.git/242277/focus=242435 > > Ah, thanks. I do remember that thread now. > > It looks like David's last word is that he gets a significant > performance from bumping the delta base cache size (and number of > buckets). Increasing number of buckets was having comparatively minor effects (that was the suggestion I started with), actually _degrading_ performance rather soon. The delta base cache size was much more noticeable. I had prepared a patch serious increasing it. The reason I have not submitted it yet is that I have not found a compelling real-world test case _apart_ from the fast git-blame that is still missing implementation of -M and -C options. There should be other commands digging through large amounts of old history, but I did not really find something benchmarking convincingly. Either most stuff is inefficient anyway, or the access order is better-behaved, causing fewer unwanted cache flushes. Access order in the optimized git-blame case is basically done with a reverse commit-time based priority queue leading to a breadth-first strategy. It still beats unsorted access solidly in its timing. Don't think I compared depth-first results (inversing the priority queue sorting condition) with regard to cache results, but it's bad for interactive use as it tends to leave some recent history unblamed for a long time while digging up stuff in the remote past. Moderate cache size increases seem like a better strategy, and the default size of 16M does not make a lot of sense with modern computers. In particular since the history digging is rarely competing with other memory intensive operations at the same time. > And that matches the timings I just did. I suspect there are still > pathological cases that could behave worse, but it really sounds like > we should be looking into improving that cache as a first step. I can put up a patch. My git-blame experiments used 128M, and the patch proposes a more conservative 64M. I don't actually have made experiments for the 64M setting, though. The current default is 16M. -- David Kastrup -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html