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diff: cache textconv output

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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>
This commit is contained in:
Jeff King
2010-04-01 20:12:15 -04:00
committed by Junio C Hamano
parent 840383b2c2
commit d9bae1a178
5 changed files with 185 additions and 9 deletions
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4
userdiff.h
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@ -1,6 +1,8 @@
#ifndef USERDIFF_H
#define USERDIFF_H
#include "notes-cache.h"
struct userdiff_funcname {
const char *pattern;
int cflags;
@ -13,6 +15,8 @@ struct userdiff_driver {
struct userdiff_funcname funcname;
const char *word_regex;
const char *textconv;
struct notes_cache *textconv_cache;
int textconv_want_cache;
};
int userdiff_config(const char *k, const char *v);