This optimizes bind_merge() and oneway_merge() to not unnecessarily
remove and re-add the old index entries when they can just get replaced
by updated ones.
This makes these operations much faster for large trees (where "large"
is in the 50,000+ file range), because we don't unnecessarily move index
entries around in the index array all the time.
Using the "bummer" tree (a test-tree with 100,000 files) we get:
Before:
[torvalds@woody bummer]$ time git commit -m"Change one file" 50/500
real 0m9.470s
user 0m8.729s
sys 0m0.476s
After:
[torvalds@woody bummer]$ time git commit -m"Change one file" 50/500
real 0m1.173s
user 0m0.720s
sys 0m0.452s
so for large trees this is easily very noticeable indeed.
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
---
Btw, these patches are based on top of my "speedup" branch, which includes
the previous changes (including the change to use "struct tree_desc" in
unpacking). However, apart from some context lines, they really should
work fine on top of current master too, so if you don't want to take the
"struct tree_desc" one, these patches should work fine even without it.
Also: this same "don't remove unnecessarily" case could (and should) be
done for the two-way and three-way cases too, and it should be trivial to
do. However, I didn't bother, since it wasn't the particular timings I was
worried about.
But doing that should help branch switching a lot, so I may send a "patch
3/2" soon.
unpack-trees.c | 6 +++---
1 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/unpack-trees.c b/unpack-trees.c
index 7fed5d2..b4e2618 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -887,7 +887,6 @@ int bind_merge(struct cache_entry **src,
struct cache_entry *old = src[0];
struct cache_entry *a = src[1];
- remove_entry(remove);
if (o->merge_size != 1)
return error("Cannot do a bind merge of %d trees\n",
o->merge_size);
@@ -912,13 +911,14 @@ int oneway_merge(struct cache_entry **src,
struct cache_entry *old = src[0];
struct cache_entry *a = src[1];
- remove_entry(remove);
if (o->merge_size != 1)
return error("Cannot do a oneway merge of %d trees",
o->merge_size);
- if (!a)
+ if (!a) {
+ remove_entry(remove);
return deleted_entry(old, old, o);
+ }
if (old && same(old, a)) {
if (o->reset) {
struct stat st;
-
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