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authorVicent Marti <tanoku@gmail.com>2013-12-21 09:00:09 -0500
committerJunio C Hamano <gitster@pobox.com>2013-12-30 12:19:22 -0800
commit6b8fda2db1d69606954711b606c546c0e4e51680 (patch)
treef6dc8c5288b36ee32f67bbdf9cc02f427594616e /Documentation/config.txt
parentce2bc42456b88c5f01f7f591cf0cc9db1a5bfc3d (diff)
downloadgit-6b8fda2db1d69606954711b606c546c0e4e51680.tar.gz
git-6b8fda2db1d69606954711b606c546c0e4e51680.tar.xz
pack-objects: use bitmaps when packing objects
In this patch, we use the bitmap API to perform the `Counting Objects` phase in pack-objects, rather than a traditional walk through the object graph. For a reasonably-packed large repo, the time to fetch and clone is often dominated by the full-object revision walk during the Counting Objects phase. Using bitmaps can reduce the CPU time required on the server (and therefore start sending the actual pack data with less delay). For bitmaps to be used, the following must be true: 1. We must be packing to stdout (as a normal `pack-objects` from `upload-pack` would do). 2. There must be a .bitmap index containing at least one of the "have" objects that the client is asking for. 3. Bitmaps must be enabled (they are enabled by default, but can be disabled by setting `pack.usebitmaps` to false, or by using `--no-use-bitmap-index` on the command-line). If any of these is not true, we fall back to doing a normal walk of the object graph. Here are some sample timings from a full pack of `torvalds/linux` (i.e. something very similar to what would be generated for a clone of the repository) that show the speedup produced by various methods: [existing graph traversal] $ time git pack-objects --all --stdout --no-use-bitmap-index \ </dev/null >/dev/null Counting objects: 3237103, done. Compressing objects: 100% (508752/508752), done. Total 3237103 (delta 2699584), reused 3237103 (delta 2699584) real 0m44.111s user 0m42.396s sys 0m3.544s [bitmaps only, without partial pack reuse; note that pack reuse is automatic, so timing this required a patch to disable it] $ time git pack-objects --all --stdout </dev/null >/dev/null Counting objects: 3237103, done. Compressing objects: 100% (508752/508752), done. Total 3237103 (delta 2699584), reused 3237103 (delta 2699584) real 0m5.413s user 0m5.604s sys 0m1.804s [bitmaps with pack reuse (what you get with this patch)] $ time git pack-objects --all --stdout </dev/null >/dev/null Reusing existing pack: 3237103, done. Total 3237103 (delta 0), reused 0 (delta 0) real 0m1.636s user 0m1.460s sys 0m0.172s Signed-off-by: Vicent Marti <tanoku@gmail.com> Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'Documentation/config.txt')
-rw-r--r--Documentation/config.txt6
1 files changed, 6 insertions, 0 deletions
diff --git a/Documentation/config.txt b/Documentation/config.txt
index ab26963d6..a9813691b 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -1858,6 +1858,12 @@ pack.packSizeLimit::
Common unit suffixes of 'k', 'm', or 'g' are
supported.
+pack.useBitmaps::
+ When true, git will use pack bitmaps (if available) when packing
+ to stdout (e.g., during the server side of a fetch). Defaults to
+ true. You should not generally need to turn this off unless
+ you are debugging pack bitmaps.
+
pager.<cmd>::
If the value is boolean, turns on or off pagination of the
output of a particular Git subcommand when writing to a tty.