Re: We should add a "git gc --auto" after "git clone" due to commit graph

SZEDER Gábor [off-list ref] writes:

There is certainly potential there.  With a (very) rough PoC
experiment, a 8MB bloom filter, and a carefully choosen path I can
achieve a nice, almost 25x speedup:

  $ time git rev-list --count HEAD -- t/valgrind/valgrind.sh
  6

  real    0m1.563s
  user    0m1.519s
  sys     0m0.045s

  $ time GIT_USE_POC_BLOOM_FILTER=y ~/src/git/git rev-list --count HEAD -- t/valgrind/valgrind.sh
  6

  real    0m0.063s
  user    0m0.043s
  sys     0m0.020s

Even though I somehow sense a sign of exaggeration in [v] in the
pathname, it still is quite respectable.

  bloom filter total queries: 16269 definitely not: 16195 maybe: 74 false positives: 64 fp ratio: 0.003934

But I'm afraid it will take a while until I get around to turn it into
something presentable...

That's OK.  This is an encouraging result.

Just from curiousity, how are you keying the filter?  tree object
name of the top-level and full path concatenated or something like
that?