Subject: [PATCH 1/6] Don't try to delta if target is much smaller than source

From: Brian Downing <[email-masked]>
Date: Thu, 12 Jul 2007 07:55:47 -0500

Add a new try_delta heuristic:  Don't bother trying to make a delta if
the target object size is much smaller (currently 1/32) than the source,
as it's very likely not going to get a match.  Even if it does, you will
have to read at least 32x the size of the new file to reassemble it,
which isn't such a good deal.  This leads to a considerable performance
improvement when deltifying a mix of small and large files with a very
large window, because you don't have to wait for the large files to
percolate out of the window before things start going fast again.

Signed-off-by: Brian Downing <[email-masked]>
---
 builtin-pack-objects.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/builtin-pack-objects.c b/builtin-pack-objects.c
index 54b9d26..132ce96 100644
--- a/builtin-pack-objects.c
+++ b/builtin-pack-objects.c
@@ -1342,6 +1342,8 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 	sizediff = src_size < trg_size ? trg_size - src_size : 0;
 	if (sizediff >= max_size)
 		return 0;
+	if (trg_size < src_size / 32)
+		return 0;
 
 	/* Load data if not already done */
 	if (!trg->data) {
-- 
1.5.2.GIT