path: root/builtin
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authorJunio C Hamano <>2013-01-08 08:02:49 (GMT)
committerJunio C Hamano <>2013-01-10 20:33:09 (GMT)
commitdf874fa82ef06c8c438b9a19c56c0b5eb089c012 (patch)
tree2e6941761add69f195ed75efc7d6cc007ae3618c /builtin
parente6bb5f78fb351c89a80826befda3c8f06f91f249 (diff)
log --use-mailmap: optimize for cases without --author/--committer search
When we taught the commit_match() mechanism to pay attention to the new --use-mailmap option, we started to unconditionally copy the commit object to a temporary buffer, just in case we need the author and committer lines updated via the mailmap mechanism, and rewrite author and committer using the mailmap. It turns out that this has a rather unpleasant performance implications. In the linux kernel repository, running $ git log --author='Junio C Hamano' --pretty=short >/dev/null under /usr/bin/time, with and without --use-mailmap (the .mailmap file is 118 entries long, the particular author does not appear in it), cost (with warm cache): [without --use-mailmap] 5.42user 0.26system 0:05.70elapsed 99%CPU (0avgtext+0avgdata 2005936maxresident)k 0inputs+0outputs (0major+137669minor)pagefaults 0swaps [with --use-mailmap] 6.47user 0.30system 0:06.78elapsed 99%CPU (0avgtext+0avgdata 2006288maxresident)k 0inputs+0outputs (0major+137692minor)pagefaults 0swaps which incurs about 20% overhead. The command is doing extra work, so the extra cost may be justified. But it is inexcusable to pay the cost when we do not need author/committer match. In the same repository, $ git log --grep='fix menuconfig on debian lenny' --pretty=short >/dev/null shows very similar numbers as the above: [without --use-mailmap] 5.32user 0.30system 0:05.63elapsed 99%CPU (0avgtext+0avgdata 2005984maxresident)k 0inputs+0outputs (0major+137672minor)pagefaults 0swaps [with --use-mailmap] 6.64user 0.24system 0:06.89elapsed 99%CPU (0avgtext+0avgdata 2006320maxresident)k 0inputs+0outputs (0major+137694minor)pagefaults 0swaps The latter case is an unnecessary performance regression. We may want to _show_ the result with mailmap applied, but we do not have to copy and rewrite the author/committer of all commits we try to match if we do not query for these fields. Trivially optimize this performace regression by limiting the rewrites for only when we are matching with author/committer fields. Signed-off-by: Junio C Hamano <>
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