don't let the delta cache grow unbounded in 'git repack'

I have 4GB of RAM on my system which should, in theory, be quite enough
to repack a 600 MB repository.  However the unbounded delta cache size
always pushes it into swap, at which point everything virtually comes to
a halt.  So unbounded caches are never a good idea.

A default of 256MB should be a good compromize between memory usage and
speed where medium sized repositories are still likely to fit in the
cache with a reasonable memory usage, and larger repositories are going
to take quite some time to repack already anyway.

While at it, clarify the associated config variable documentation
entries a bit.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/config.txt b/Documentation/config.txt
index c6f09f801a8dbb2f03e73ab5dd11c1139332fa5f..7791c32bc3461d7fcc73001165492b84c0997f06 100644 (file)
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -1218,12 +1218,20 @@ pack.compression::
 
 pack.deltaCacheSize::
        The maximum memory in bytes used for caching deltas in
-       linkgit:git-pack-objects[1].
-       A value of 0 means no limit. Defaults to 0.
+       linkgit:git-pack-objects[1] before writing them out to a pack.
+       This cache is used to speed up the writing object phase by not
+       having to recompute the final delta result once the best match
+       for all objects is found.  Repacking large repositories on machines
+       which are tight with memory might be badly impacted by this though,
+       especially if this cache pushes the system into swapping.
+       A value of 0 means no limit. The smallest size of 1 byte may be
+       used to virtually disable this cache. Defaults to 256 MiB.
 
 pack.deltaCacheLimit::
        The maximum size of a delta, that is cached in
-       linkgit:git-pack-objects[1]. Defaults to 1000.
+       linkgit:git-pack-objects[1]. This cache is used to speed up the
+       writing object phase by not having to recompute the final delta
+       result once the best match for all objects is found. Defaults to 1000.
 
 pack.threads::
        Specifies the number of threads to spawn when searching for best

diff --git a/builtin-pack-objects.c b/builtin-pack-objects.c
index ef4bf6bc14aadffcd85999c2eca59e5a0e7e6451..9cc8a8451d21840b315d1355207293a1b0bcbf2c 100644 (file)
--- a/builtin-pack-objects.c
+++ b/builtin-pack-objects.c
@@ -86,7 +86,7 @@ static int pack_compression_level = Z_DEFAULT_COMPRESSION;
 static int pack_compression_seen;
 
 static unsigned long delta_cache_size = 0;
-static unsigned long max_delta_cache_size = 0;
+static unsigned long max_delta_cache_size = 256 * 1024 * 1024;
 static unsigned long cache_max_small_delta_size = 1000;
 
 static unsigned long window_memory_limit = 0;