diff: cache textconv output
Running a textconv filter can take a long time. It's particularly bad for a large file which needs to be spooled to disk, but even for small files, the fork+exec overhead can add up for something like "git log -p". This patch uses the notes-cache mechanism to keep a fast cache of textconv output. Caches are stored in refs/notes/textconv/$x, where $x is the userdiff driver defined in gitattributes. Caching is enabled only if diff.$x.cachetextconv is true. In my test repo, on a commit with 45 jpg and avi files changed and a textconv to show their exif tags: [before] $ time git show >/dev/null real 0m13.724s user 0m12.057s sys 0m1.624s [after, first run] $ git config diff.mfo.cachetextconv true $ time git show >/dev/null real 0m14.252s user 0m12.197s sys 0m1.800s [after, subsequent runs] $ time git show >/dev/null real 0m0.352s user 0m0.148s sys 0m0.200s So for a slight (3.8%) cost on the first run, we achieve an almost 40x speed up on subsequent runs. Signed-off-by: NJeff King <peff@peff.net> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
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t/t4042-diff-textconv-caching.sh
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