This trivial patch avoids re-hashing files that are already clean in the
index. This mirrors what commit 0781b8a9b2fe760fc4ed519a3a26e4b9bd6ccffe
did for "git add .", only for "git commit ." instead.
This improves the cold-cache case immensely, since we don't need to bring
in all the file contents, just the index and any files dirty in the index.
Before:
[torvalds@woody linux]$ time git commit .
real 1m49.537s
user 0m3.892s
sys 0m2.432s
After:
[torvalds@woody linux]$ time git commit .
real 0m14.273s
user 0m1.312s
sys 0m0.516s
(both after doing a "echo 3 > /proc/sys/vm/drop_caches" to get cold-cache
behaviour - even with the index optimization git still has to "lstat()"
all the files, so with a truly cold cache, bringing all the inodes in
will take some time).
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
---
On Fri, 10 Aug 2007, Linus Torvalds wrote:
>
> Try this on the kernel archive (use a clean one, so these things *should*
> all be no-ops):
>
> time sh -c "git add . ; git commit"
>
> which is nice and fast and takes just over a second for me, but then try
>
> time git commit .
>
> which *should* be nice and fast, but it takes forever, because we now
> re-compute all the SHA1's for *every* file. Of course, if it's all in the
> cache, it's still just 4s for me, but I tried with a cold cache, and it
> was over half a minute!
>
> (I don't actually ever do something like "git commit .", but I could see
> people doing it. What I *do* do is that if I have multiple independent
> changes, I may actually do "git commit fs" to commit just part of them,
> and rather than list all the files, I literally just say "commit that
> sub-tree". So this really is another valid performance issue).
>
> Sad.
>
> Linus
>
---
builtin-update-index.c | 10 ++++++++--
1 files changed, 8 insertions(+), 2 deletions(-)
diff --git a/builtin-update-index.c b/builtin-update-index.c
index 509369e..8d22dfa 100644
--- a/builtin-update-index.c
+++ b/builtin-update-index.c
@@ -86,9 +86,15 @@ static int process_lstat_error(const char *path, int err)
static int add_one_path(struct cache_entry *old, const char *path, int len, struct stat *st)
{
- int option, size = cache_entry_size(len);
- struct cache_entry *ce = xcalloc(1, size);
+ int option, size;
+ struct cache_entry *ce;
+
+ /* Was the old index entry already up-to-date? */
+ if (old && !ce_stage(old) && !ce_match_stat(old, st, 0))
+ return;
+ size = cache_entry_size(len);
+ ce = xcalloc(1, size);
memcpy(ce->name, path, len);
ce->ce_flags = htons(len);
fill_stat_cache_info(ce, st);
-
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