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cat-file: provide %(deltabase) batch format

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It can be useful for debugging or analysis to see which
objects are stored as delta bases on top of others. This
information is available by running `git verify-pack`, but
that is extremely expensive (and is harder than necessary to
parse).

Instead, let's make it available as a cat-file query format,
which makes it fast and simple to get the bases for a subset
of the objects.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff King 2013-12-21 09:25:22 -05:00 committed by Junio C Hamano
parent 5d642e7506
commit 65ea9c3c3d
3 changed files with 49 additions and 3 deletions
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12
Documentation/git-cat-file.txt
View File

@ -109,6 +109,11 @@ newline. The available atoms are:
The size, in bytes, that the object takes up on disk. See the
note about on-disk sizes in the `CAVEATS` section below.
`deltabase`::
If the object is stored as a delta on-disk, this expands to the
40-hex sha1 of the delta base object. Otherwise, expands to the
null sha1 (40 zeroes). See `CAVEATS` below.
`rest`::
If this atom is used in the output string, input lines are split
at the first whitespace boundary. All characters before that
@ -152,10 +157,11 @@ should be taken in drawing conclusions about which refs or objects are
responsible for disk usage. The size of a packed non-delta object may be
much larger than the size of objects which delta against it, but the
choice of which object is the base and which is the delta is arbitrary
and is subject to change during a repack. Note also that multiple copies
of an object may be present in the object database; in this case, it is
undefined which copy's size will be reported.
and is subject to change during a repack.
Note also that multiple copies of an object may be present in the object
database; in this case, it is undefined which copy's size or delta base
will be reported.
GIT
---

6
builtin/cat-file.c
View File

@ -118,6 +118,7 @@ struct expand_data {
unsigned long size;
unsigned long disk_size;
const char *rest;
unsigned char delta_base_sha1[20];
/*
* If mark_query is true, we do not expand anything, but rather
@ -174,6 +175,11 @@ static void expand_atom(struct strbuf *sb, const char *atom, int len,
data->split_on_whitespace = 1;
else if (data->rest)
strbuf_addstr(sb, data->rest);
} else if (is_atom("deltabase", atom, len)) {
if (data->mark_query)
data->info.delta_base_sha1 = data->delta_base_sha1;
else
strbuf_addstr(sb, sha1_to_hex(data->delta_base_sha1));
} else
die("unknown format element: %.*s", len, atom);
}

34
t/t1006-cat-file.sh
View File

@ -240,4 +240,38 @@ test_expect_success "--batch-check with multiple sha1s gives correct format" '
"$(echo_without_newline "$batch_check_input" | git cat-file --batch-check)"
'
test_expect_success 'setup blobs which are likely to delta' '
test-genrandom foo 10240 >foo &&
{ cat foo; echo plus; } >foo-plus &&
git add foo foo-plus &&
git commit -m foo &&
cat >blobs <<-\EOF
HEAD:foo
HEAD:foo-plus
EOF
'
test_expect_success 'confirm that neither loose blob is a delta' '
cat >expect <<-EOF
$_z40
$_z40
EOF
git cat-file --batch-check="%(deltabase)" <blobs >actual &&
test_cmp expect actual
'
# To avoid relying too much on the current delta heuristics,
# we will check only that one of the two objects is a delta
# against the other, but not the order. We can do so by just
# asking for the base of both, and checking whether either
# sha1 appears in the output.
test_expect_success '%(deltabase) reports packed delta bases' '
git repack -ad &&
git cat-file --batch-check="%(deltabase)" <blobs >actual &&
{
grep "$(git rev-parse HEAD:foo)" actual ||
grep "$(git rev-parse HEAD:foo-plus)" actual
}
'
test_done