The default of 16m causes serious thrashing for large delta chains
combined with large files.
Here are some benchmarks (pu variant of git blame):
time git blame -C src/xdisp.c >/dev/null
for a repository of Emacs repacked with git gc --aggressive (v1.9,
resulting in a window size of 250) located on an SSD drive. The file in
question has about 30000 lines, 1Mb of size, and a history with about
2500 commits.
16m (previous default):
real 3m33.936s
user 2m15.396s
sys 1m17.352s
32m:
real 3m1.319s
user 2m8.660s
sys 0m51.904s
64m:
real 2m20.636s
user 1m55.780s
sys 0m23.964s
96m:
real 2m5.668s
user 1m50.784s
sys 0m14.288s
128m:
real 2m4.337s
user 1m50.764s
sys 0m12.832s
192m:
real 2m3.567s
user 1m49.508s
sys 0m13.312s
Signed-off-by: David Kastrup <d...@gnu.org>
---
Documentation/config.txt | 2 +-
environment.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/Documentation/config.txt b/Documentation/config.txt
index 1932e9b..21a3c86 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -489,7 +489,7 @@ core.deltaBaseCacheLimit::
to avoid unpacking and decompressing frequently used base
objects multiple times.
+
-Default is 16 MiB on all platforms. This should be reasonable
+Default is 96 MiB on all platforms. This should be reasonable
for all users/operating systems, except on the largest projects.
You probably do not need to adjust this value.
+
diff --git a/environment.c b/environment.c
index 5c4815d..37354c8 100644
--- a/environment.c
+++ b/environment.c
@@ -37,7 +37,7 @@ int core_compression_seen;
int fsync_object_files;
size_t packed_git_window_size = DEFAULT_PACKED_GIT_WINDOW_SIZE;
size_t packed_git_limit = DEFAULT_PACKED_GIT_LIMIT;
-size_t delta_base_cache_limit = 16 * 1024 * 1024;
+size_t delta_base_cache_limit = 96 * 1024 * 1024;
unsigned long big_file_threshold = 512 * 1024 * 1024;
const char *pager_program;
int pager_use_color = 1;
--
1.9.1
--
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