On Fri, Mar 30, 2018 at 10:59 PM, Jeff King <peff@xxxxxxxx> wrote: > On Sat, Mar 24, 2018 at 07:33:48AM +0100, Nguyễn Thái Ngọc Duy wrote: > >> We only cache deltas when it's smaller than a certain limit. This limit >> defaults to 1000 but save its compressed length in a 64-bit field. >> Shrink that field down to 16 bits, so you can only cache 65kb deltas. >> Larger deltas must be recomputed at when the pack is written down. > > Unlike the depth, I don't think there's any _inherent_ reason you > couldn't throw, say, 1MB deltas into the cache (if you sized it large > enough). But I doubt such deltas are really all that common. Here are > the top 10 in linux.git: > > $ git cat-file --batch-all-objects --batch-check='%(deltabase) %(objectsize:disk)' | > grep -v ^00000 | sort -k 2nr | head > a02b6794337286bc12c907c33d5d75537c240bd0 769103 > b28d4b64c05da02c5e8c684dcb9422876225ebdc 327116 > 1e98ce86ed19aff9ba721d13a749ff08088c9922 325257 > a02b6794337286bc12c907c33d5d75537c240bd0 240647 > c550d99286c01867dfb26e432417f3106acf8611 177896 > 5977795854f852c2b95dd023fd03cace023ee41c 119737 > 4ccf9681c45d01d17376f7e0d266532a4460f5f8 112671 > b39fb6821faa9e7bc36de738152a2817b4bf3654 112657 > 2645d6239b74bebd661436762e819b831095b084 103980 > b8ce7fe5d8def58dc63b7ae099eff7bd07e4e845 101014 > > It's possible some weird workload would want to tweak this. Say you were > storing a ton of delta-capable files that were big and always differed > by a megabyte. And it was somehow really important to you to tradeoff > memory for CPU during the write phase of a pack. We're not short on spare bits so I will try to raise this limit to 1MB (not because you mentioned 1MB, but because the largest size in your output is close to 1MB). -- Duy
