When fast-export wants to export a blob object, it first
calls parse_object to get a "struct object" and check
whether we have already shown the object. If we haven't
shown it, we then use read_sha1_file to pull it from disk
and write it out.
That means we load each blob from disk twice: once for
parse_object to find its type and check its sha1, and a
second time when we actually output it. We can drop this to
a single load by using lookup_object to check the SHOWN
flag, and then checking the signature on and outputting a
single buffer.
This provides modest speedups on git.git (best-of-five, "git
fast-export HEAD >/dev/null"):
[before] [after]
real 0m14.347s real 0m13.780s
user 0m14.084s user 0m13.620s
sys 0m0.208s sys 0m0.100s
and somewhat more on more blob-heavy repos (this is a
repository full of media files):
[before] [after]
real 0m52.236s real 0m44.451s
user 0m50.568s user 0m43.000s
sys 0m1.536s sys 0m1.284s
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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