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.
That seems pretty unlikely to bite anybody (and that was the best I
could come up with as a devil's advocate against it).
> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@xxxxxxxxx>
> ---
> Documentation/config.txt | 3 ++-
> builtin/pack-objects.c | 22 ++++++++++++++++------
> pack-objects.h | 3 ++-
> 3 files changed, 20 insertions(+), 8 deletions(-)
Patch looks OK.
-Peff
