[PATCH/RFC] clone: suggest index version 4 when the index is bigger than 512 KiB

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

I just realized that many of my big repos are still on index v2 while
v4 should reduce its size significantly (3.8M -> 2.9M for linux-2.6
and 25M -> 14M for webkit, for example). I wanted to propose index v4
as the new default version, because I guess that not many people
outside git@vger are aware of it, but perhaps this approach is less
drastic. It only suggest index v4 when the index size after clone hits
512K limit.

I have 170 git repositories (most of them Gnome projects) and only big
ones exceed the limit: webkit, linux-2.6, libreoffice-core, wine
(530K), gentoo-x86. Gimp and banshee are close (510K and 321K). The
rest barely hits 256K. So this hint won't show up often. On second
thought, maybe we should lower it down to 300K to show more often and
raise awareness on index v4 :)

Something I should have done in this patch too, is state that index v4
is only supported since vXXX, that git clients older than that will
not work. But maybe just put that in update-index man page and refer
there.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 builtin/clone.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/builtin/clone.c b/builtin/clone.c
index e0aaf13..7cd1b60 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -543,6 +543,7 @@ static int checkout(void)
 	struct tree *tree;
 	struct tree_desc t;
 	int err = 0, fd;
+	struct stat st;
 
 	if (option_no_checkout)
 		return 0;
@@ -591,6 +592,15 @@ static int checkout(void)
 	if (!err && option_recursive)
 		err = run_command_v_opt(argv_submodule, RUN_GIT_CMD);
 
+	if (!err &&
+	    !stat(git_path("index"), &st) &&
+	    st.st_size > 512 * 1024)
+		advise(_("Your index is quite large (%d KiB).\n"
+			 "You may want to update to index version 4 to reduce its size,\n"
+			"as large index files may affect performance, using the command:\n"
+			 "  git update-index --index-version 4"),
+		       st.st_size / 1024);
+
 	return err;
 }
 
-- 
1.8.1.2.536.gf441e6d