[PATCH 3/3] builtin-pack-object: cache small deltas

[Martin Koegler <mkoegler@auto.tuwien.ac.at>]

Signed-off-by: Martin Koegler <mkoegler@auto.tuwien.ac.at>
---
Caching small deltas improves packing time even on small repostistories.
Repacking git.git with a delta size limit of 1000 brings CPU time from
66 to 49 seconds down. A limit of 500 bytes is only two secondes slower.

The implicit cache size limit is (#objects)*(delta size limit).

 Documentation/config.txt |    4 ++++
 builtin-pack-objects.c   |    8 ++++++++
 2 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 83cc4cd..0061f7f 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -572,6 +572,10 @@ pack.deltaCacheSize::
 	gitlink:git-pack-objects[1]. 	
 	A value of 0 means no limit. Defaults to 0.
 
+pack.deltaCacheLimit::
+	The maxium size of a delta, that is cached in 
+	gitlink:git-pack-objects[1]. Defaults to 1000.
+
 pull.octopus::
 	The default merge strategy to use when pulling multiple branches
 	at once.
diff --git a/builtin-pack-objects.c b/builtin-pack-objects.c
index 85e08dc..c316fea 100644
--- a/builtin-pack-objects.c
+++ b/builtin-pack-objects.c
@@ -79,6 +79,7 @@ static int pack_compression_seen;
 
 static unsigned long delta_cache_size = 0;
 static unsigned long max_delta_cache_size = 0;
+static unsigned long cache_max_small_delta_size = 1000;
 
 /*
  * The object names in objects array are hashed with this hashtable,
@@ -1403,6 +1404,9 @@ static int delta_cacheable (struct unpacked *trg, struct unpacked *src,
 	if (max_delta_cache_size && delta_cache_size + delta_size > max_delta_cache_size)
 		return 0;
 
+	if (delta_size < cache_max_small_delta_size) 
+		return 1;
+
 	/* cache delta, if objects are large enough compared to delta size */
 	if ((src_size >> 20) + (trg_size >> 21) > (delta_size >> 10))
 		return 1;
@@ -1654,6 +1658,10 @@ static int git_pack_config(const char *k, const char *v)
 		max_delta_cache_size = git_config_int(k, v);
 		return 0;
 	}
+	if(!strcmp(k, "pack.deltacachelimit")) {
+		cache_max_small_delta_size = git_config_int(k, v);
+		return 0;
+	}
 	return git_default_config(k, v);
 }
 
-- 
1.5.2.846.g9a144