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authorLibravatar Jeff King <peff@peff.net>2010-04-01 20:14:24 -0400
committerLibravatar Junio C Hamano <gitster@pobox.com>2010-04-02 00:11:20 -0700
commitb3373982667dc983b8dacf33861d25b20bafb995 (patch)
tree852fb52d64888301061e03ec99f4906385cb3aa9 /builtin/help.c
parentdiff: cache textconv output (diff)
downloadtgif-b3373982667dc983b8dacf33861d25b20bafb995.tar.xz
diff: avoid useless filespec population
builtin_diff calls fill_mmfile fairly early, which in turn calls diff_populate_filespec, which actually retrieves the file's blob contents into a buffer. Long ago, this was sensible as we would need to look at the blobs eventually. These days, however, we may not ever want those blobs if we end up using a textconv cache, and for large binary files (exactly the sort for which you might have a textconv cache), just retrieving the objects can be costly. This patch just pushes the fill_mmfile call a bit later, so we can avoid populating the filespec in some cases. There is one thing to note that looks like a bug but isn't. We push the fill_mmfile down into the first branch of a conditional. It seems like we would need it on the other branch, too, but we don't; fill_textconv does it for us (in fact, before this, we were just writing over the results of the fill_mmfile on that branch). Here's a timing sample on a commit with 45 changed jpgs and avis. The result is fully textconv cached, but we still wasted a lot of time just pulling the blobs from storage. The total size of the blobs (source and dest) is about 180M. [before] $ time git show >/dev/null real 0m0.352s user 0m0.148s sys 0m0.200s [after] $ time git show >/dev/null real 0m0.009s user 0m0.004s sys 0m0.004s And that's on a warm cache. On a cold cache, the "after" case is not much worse, but the "before" case has to do an extra 180M of I/O. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
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