doc/git-gc: add a note about what is collected

It seems to be a FAQ that people try running git-gc, and
then get puzzled about why the size of their .git directory
didn't change. This note mentions the reasons why things
might unexpectedly get kept.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/git-gc.txt b/Documentation/git-gc.txt
index d424a4ecbe2c751550f50048e63ce640941a3ebb..b6b5ce15199ebfa8f92bff8586d04e502aa23b86 100644 (file)
--- a/Documentation/git-gc.txt
+++ b/Documentation/git-gc.txt
@@ -104,6 +104,21 @@ The optional configuration variable 'gc.pruneExpire' controls how old
 the unreferenced loose objects have to be before they are pruned.  The
 default is "2 weeks ago".
 
 the unreferenced loose objects have to be before they are pruned.  The
 default is "2 weeks ago".
 

+
+Notes
+-----
+
+git-gc tries very hard to be safe about the garbage it collects. In
+particular, it will keep not only objects referenced by your current set
+of branches and tags, but also objects referenced by the index, remote
+tracking branches, refs saved by linkgit:git-filter-branch[1] in
+refs/original/, or reflogs (which may references commits in branches
+that were later amended or rewound).
+
+If you are expecting some objects to be collected and they aren't, check
+all of those locations and decide whether it makes sense in your case to
+remove those references.
+

 See Also
 --------
 linkgit:git-prune[1]
 See Also
 --------
 linkgit:git-prune[1]