Re: [PATCH v5] pack-objects: teach it to use reachability bitmap index when generating non-stdout pack too

On Mon, Aug 08, 2016 at 01:53:20PM -0700, Junio C Hamano wrote:

Kirill Smelkov [off-list ref] writes:

quoted

diff --git a/Documentation/config.txt b/Documentation/config.txt
index bc1c433..4ba0c4a 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt

@@ -2244,6 +2244,9 @@ pack.useBitmaps::
 	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.
++
+*NOTE*: when packing to file (e.g., on repack) the default is always not to use
+	pack bitmaps.

This is a bit hard to read and understand.

The patched result starts with "When true, git will use bitmap when
packing to stdout", i.e. when packing to file, git will not.  So
this *NOTE* is repeating the same thing.  The reader is made to
wonder "Why does it need to repeat the same thing?  Does this mean
when the variable is set, a pack sent to a disk uses the bitmap?"

I think what you actually do in the code is to make the variable
affect _only_ the standard-output case, and users need a command
line option if they want to use bitmap when writing to a file (the
code to do so looks correctly done).

Yes it is this way how it is programmed. But I've added the note because
it is very implicit to me that "When true, git will use bitmap when
packing to stdout" means 1) the default for packing-to-file is different
and 2) there is no way to set the default for packing-to-file. That's
why I added the explicit info.

And especially since the config name "pack.useBitmaps" does not contain
"stdout" at all it can be very confusing to people looking at this the
first time (at least it was so this way for me). Also please recall you
wondering why 6b8fda2d added bitmap support only for to-stdout case not
even mentioning about why it is done only for that case and not for
to-file case).

I do not insist on the note however - I only thought it is better to
have it - so if you prefer we go without it - let us drop this note.

Will send v6 as reply to this mail with below interdiff.

Thanks,
Kirill

---- 8< ---- (interdiff)

--- b/Documentation/config.txt
+++ a/Documentation/config.txt

@@ -2246,9 +2246,6 @@
        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.
-+
-*NOTE*: when packing to file (e.g., on repack) the default is always not to use
-       pack bitmaps.
 
 pack.writeBitmaps (deprecated)::
        This is a deprecated synonym for `repack.writeBitmaps`.

diff -u b/t/t5310-pack-bitmaps.sh b/t/t5310-pack-bitmaps.sh

--- b/t/t5310-pack-bitmaps.sh
+++ b/t/t5310-pack-bitmaps.sh

@@ -219,8 +219,8 @@
        # verify equivalent packs are generated with/without using bitmap index
        packasha1=$(git pack-objects --no-use-bitmap-index --all packa </dev/null) &&
        packbsha1=$(git pack-objects --use-bitmap-index --all packb </dev/null) &&
-       git show-index <packa-$packasha1.idx | cut -d" " -f2 >packa.objects &&
-       git show-index <packb-$packbsha1.idx | cut -d" " -f2 >packb.objects &&
+       pack_list_objects <packa-$packasha1.idx >packa.objects &&
+       pack_list_objects <packb-$packbsha1.idx >packb.objects &&
        test_cmp packa.objects packb.objects
 '