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: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
