From: Taylor Blau <me@ttaylorr.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: Jonathan Tan <jonathantanmy@google.com>,
git@vger.kernel.org, Derrick Stolee <derrickstolee@github.com>
Subject: Re: [PATCH v6 0/7] Changed path filter hash fix and version bump
Date: Wed, 26 Jul 2023 20:17:20 -0400 [thread overview]
Message-ID: <ZMG3kEO0BzKPaG75@nand.local> (raw)
In-Reply-To: <xmqq8rb2csr1.fsf@gitster.g>
On Wed, Jul 26, 2023 at 01:39:14PM -0700, Junio C Hamano wrote:
> Jonathan Tan <jonathantanmy@google.com> writes:
>
> > Jonathan Tan (4):
> > gitformat-commit-graph: describe version 2 of BDAT
> > t4216: test changed path filters with high bit paths
> > repo-settings: introduce commitgraph.changedPathsVersion
> > commit-graph: new filter ver. that fixes murmur3
> >
> > Taylor Blau (3):
> > t/helper/test-read-graph.c: extract `dump_graph_info()`
> > bloom.h: make `load_bloom_filter_from_graph()` public
> > t/helper/test-read-graph: implement `bloom-filters` mode
>
> After a week, nobody seems to have found anything worth saying about
> these patches. Does the design, especially the migration story, now
> look sensible to everybody? I was contemplating to mark the topic
> for 'next' after reading them myself once more.
Sorry for not getting to this sooner. I didn't notice anything during my
review, but I think there may be a bug here.
Suppose that we have an existing commit-graph with v1 Bloom filters. If
we then try to rewrite that commit-graph using v2 Bloom filters, we
*should* attempt to recompute the filter from scratch. But AFAICT, that
isn't what happens.
Here's my test setup:
test_expect_success 'test' '
test_commit base &&
git repack -d &&
git -c commitGraph.changedPathVersion=1 commit-graph write --changed-paths &&
debug git -c commitGraph.changedPathVersion=2 commit-graph write --changed-paths
'
if you attach a debugger to the second process, and break inside of
get_or_compute_bloom_filter() when compute_if_not_present is set, you'll
see that Git will pass along the existing *v1* Bloom filter, and then
write its contents to the new commit-graph:
(gdb) b get_or_compute_bloom_filter if compute_if_not_present
Breakpoint 1 at 0x14340f: file bloom.c, line 260.
(gdb) r
Starting program: /home/ttaylorr/src/git/git -c commitGraph.changedPathVersion=2 commit-graph write --changed-paths
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Breakpoint 1, get_or_compute_bloom_filter (r=0x5555559bdc80 <the_repo>, c=0x5555559c8ef0,
compute_if_not_present=1, settings=0x5555559c6950, computed=0x7fffffffd854) at bloom.c:260
260 if (computed)
(gdb) until 271
get_or_compute_bloom_filter (r=0x5555559bdc80 <the_repo>, c=0x5555559c8ef0, compute_if_not_present=1,
settings=0x5555559c6950, computed=0x7fffffffd854) at bloom.c:271
271 load_bloom_filter_from_graph(r->objects->commit_graph,
(gdb) p *filter
$2 = {data = 0x0, len = 0}
(gdb) n
275 if (filter->data && filter->len)
(gdb) p *filter
$3 = {data = 0x7ffff7fc24a8 "\210\210\322a\267\234\214s}\004J\265\313\201\241\032e\312\034", len = 2}
If I'm parsing this all correctly, Git used the v1 filter corresponding
to that commit, and did not recompute a new one.
I think that this could lead to incorrect results if you use this to
masquerade a v1 Bloom filter as a v2 one. Since they use different
implementations (one correct, one not) of murmur3, that opens us up to
false negatives, at which point all bets are off.
So I think we want to be more careful about when we load the existing
Bloom data or not. I think we probably want to load it in all cases, but
only read it when we have compatible Bloom settings. That should stop us
from exhibiting this kind of bug, but it also gives us a handle on
existing Bloom data if we wanted to copy forward existing results where
we can.
If all of this tracks, I think that there is a gap in our test coverage
that didn't catch this earlier.
Thanks,
Taylor
next prev parent reply other threads:[~2023-07-27 0:17 UTC|newest]
Thread overview: 116+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-22 21:48 [PATCH 0/2] Changed path filter hash fix and version bump Jonathan Tan
2023-05-22 21:48 ` [PATCH 1/2] t4216: test wrong bloom filter version rejection Jonathan Tan
2023-05-22 21:48 ` [PATCH 2/2] commit-graph: fix murmur3, bump filter ver. to 2 Jonathan Tan
2023-05-23 13:00 ` Derrick Stolee
2023-05-23 23:00 ` Jonathan Tan
2023-05-23 23:51 ` Junio C Hamano
2023-05-24 21:26 ` Jonathan Tan
2023-05-26 13:19 ` Derrick Stolee
2023-05-30 17:26 ` Jonathan Tan
2023-05-23 4:42 ` [PATCH 0/2] Changed path filter hash fix and version bump Junio C Hamano
2023-05-31 23:12 ` [PATCH v2 0/3] " Jonathan Tan
2023-05-31 23:12 ` [PATCH v2 1/3] t4216: test changed path filters with high bit paths Jonathan Tan
2023-05-31 23:12 ` [PATCH v2 2/3] repo-settings: introduce commitgraph.changedPathsVersion Jonathan Tan
2023-05-31 23:12 ` [PATCH v2 3/3] commit-graph: new filter ver. that fixes murmur3 Jonathan Tan
2023-06-03 1:01 ` [PATCH v2 0/3] Changed path filter hash fix and version bump Junio C Hamano
2023-06-03 2:24 ` Junio C Hamano
2023-06-07 16:30 ` Jonathan Tan
2023-06-07 21:37 ` Jonathan Tan
2023-06-08 19:21 ` [PATCH v3 0/4] " Jonathan Tan
2023-06-08 19:21 ` [PATCH v3 1/4] gitformat-commit-graph: describe version 2 of BDAT Jonathan Tan
2023-06-08 19:52 ` Ramsay Jones
2023-06-12 21:26 ` Junio C Hamano
2023-06-08 19:21 ` [PATCH v3 2/4] t4216: test changed path filters with high bit paths Jonathan Tan
2023-06-08 19:21 ` [PATCH v3 3/4] repo-settings: introduce commitgraph.changedPathsVersion Jonathan Tan
2023-06-08 19:21 ` [PATCH v3 4/4] commit-graph: new filter ver. that fixes murmur3 Jonathan Tan
2023-06-08 19:50 ` [PATCH v3 0/4] Changed path filter hash fix and version bump Ramsay Jones
2023-06-09 0:08 ` Jonathan Tan
2023-06-12 21:31 ` Junio C Hamano
2023-06-13 17:16 ` Jonathan Tan
2023-06-13 17:29 ` [PATCH] CodingGuidelines: use octal escapes, not hex Jonathan Tan
2023-06-13 18:16 ` Eric Sunshine
2023-06-13 18:43 ` Jonathan Tan
2023-06-13 19:15 ` Eric Sunshine
2023-06-13 19:29 ` Junio C Hamano
2023-06-13 19:16 ` [PATCH v3 0/4] Changed path filter hash fix and version bump Junio C Hamano
2023-06-13 17:39 ` [PATCH v4 " Jonathan Tan
2023-06-13 17:39 ` [PATCH v4 1/4] gitformat-commit-graph: describe version 2 of BDAT Jonathan Tan
2023-06-13 21:58 ` Junio C Hamano
2023-06-20 13:22 ` Derrick Stolee
2023-06-21 12:08 ` Taylor Blau
2023-06-22 22:26 ` Jonathan Tan
2023-06-23 13:05 ` Derrick Stolee
2023-06-13 17:39 ` [PATCH v4 2/4] t4216: test changed path filters with high bit paths Jonathan Tan
2023-06-13 17:39 ` [PATCH v4 3/4] repo-settings: introduce commitgraph.changedPathsVersion Jonathan Tan
2023-06-20 13:28 ` Derrick Stolee
2023-06-21 12:14 ` Taylor Blau
2023-06-13 17:39 ` [PATCH v4 4/4] commit-graph: new filter ver. that fixes murmur3 Jonathan Tan
2023-06-20 13:39 ` Derrick Stolee
2023-06-20 18:37 ` Junio C Hamano
2023-06-13 19:21 ` [PATCH v4 0/4] Changed path filter hash fix and version bump Junio C Hamano
2023-06-20 13:43 ` Derrick Stolee
2023-06-20 21:56 ` Jonathan Tan
2023-06-21 12:19 ` Taylor Blau
2023-06-21 17:53 ` Derrick Stolee
2023-06-22 22:27 ` Jonathan Tan
2023-06-23 13:18 ` Derrick Stolee
2023-07-13 21:42 ` [PATCH v5 " Jonathan Tan
2023-07-13 21:42 ` [PATCH v5 1/4] gitformat-commit-graph: describe version 2 of BDAT Jonathan Tan
2023-07-19 17:25 ` Taylor Blau
2023-07-20 20:20 ` Jonathan Tan
2023-07-21 1:38 ` Taylor Blau
2023-07-13 21:42 ` [PATCH v5 2/4] t4216: test changed path filters with high bit paths Jonathan Tan
2023-07-13 22:50 ` Junio C Hamano
2023-07-19 17:27 ` Taylor Blau
2023-07-19 17:55 ` [PATCH 0/4] commit-graph: avoid looking at Bloom filter data directly Taylor Blau
2023-07-19 17:55 ` [PATCH 1/4] t/helper/test-read-graph.c: extract `dump_graph_info()` Taylor Blau
2023-07-19 17:55 ` [PATCH 2/4] bloom.h: make `load_bloom_filter_from_graph()` public Taylor Blau
2023-07-19 17:55 ` [PATCH 3/4] t/helper/test-read-graph: implement `bloom-filters` mode Taylor Blau
2023-07-19 17:55 ` [PATCH 4/4] fixup! t4216: test changed path filters with high bit paths Taylor Blau
2023-07-19 19:24 ` [PATCH 0/4] commit-graph: avoid looking at Bloom filter data directly Junio C Hamano
2023-07-20 20:22 ` Jonathan Tan
2023-07-13 21:42 ` [PATCH v5 3/4] repo-settings: introduce commitgraph.changedPathsVersion Jonathan Tan
2023-07-19 18:10 ` Taylor Blau
2023-07-20 20:42 ` Jonathan Tan
2023-07-20 21:02 ` Taylor Blau
2023-07-13 21:42 ` [PATCH v5 4/4] commit-graph: new filter ver. that fixes murmur3 Jonathan Tan
2023-07-19 18:24 ` Taylor Blau
2023-07-20 21:27 ` Jonathan Tan
2023-07-26 23:32 ` Taylor Blau
2023-07-13 22:16 ` [PATCH v5 0/4] Changed path filter hash fix and version bump Junio C Hamano
2023-07-13 22:59 ` Junio C Hamano
2023-07-14 18:48 ` Jonathan Tan
2023-07-20 21:46 ` [PATCH v6 0/7] " Jonathan Tan
2023-07-20 21:46 ` [PATCH v6 1/7] gitformat-commit-graph: describe version 2 of BDAT Jonathan Tan
2023-07-20 21:46 ` [PATCH v6 2/7] t/helper/test-read-graph.c: extract `dump_graph_info()` Jonathan Tan
2023-07-26 23:26 ` Taylor Blau
2023-07-20 21:46 ` [PATCH v6 3/7] bloom.h: make `load_bloom_filter_from_graph()` public Jonathan Tan
2023-07-20 21:46 ` [PATCH v6 4/7] t/helper/test-read-graph: implement `bloom-filters` mode Jonathan Tan
2023-07-20 21:46 ` [PATCH v6 5/7] t4216: test changed path filters with high bit paths Jonathan Tan
2023-07-26 23:28 ` Taylor Blau
2023-07-20 21:46 ` [PATCH v6 6/7] repo-settings: introduce commitgraph.changedPathsVersion Jonathan Tan
2023-07-20 21:46 ` [PATCH v6 7/7] commit-graph: new filter ver. that fixes murmur3 Jonathan Tan
2023-07-25 20:52 ` [PATCH v6 0/7] Changed path filter hash fix and version bump Junio C Hamano
2023-07-26 20:39 ` Junio C Hamano
2023-07-27 0:17 ` Taylor Blau [this message]
2023-07-27 0:49 ` Junio C Hamano
2023-07-27 17:39 ` Jonathan Tan
2023-07-27 17:56 ` Taylor Blau
2023-07-27 20:53 ` Jonathan Tan
2023-08-01 18:08 ` Taylor Blau
2023-08-01 18:52 ` Jonathan Tan
2023-08-03 0:01 ` Taylor Blau
2023-08-03 13:18 ` Derrick Stolee
2023-08-03 18:45 ` Taylor Blau
2023-07-27 18:44 ` Junio C Hamano
2023-08-01 18:41 ` [PATCH v7 " Jonathan Tan
2023-08-01 18:41 ` [PATCH v7 1/7] gitformat-commit-graph: describe version 2 of BDAT Jonathan Tan
2023-08-01 18:41 ` [PATCH v7 2/7] t/helper/test-read-graph.c: extract `dump_graph_info()` Jonathan Tan
2023-08-01 18:41 ` [PATCH v7 3/7] bloom.h: make `load_bloom_filter_from_graph()` public Jonathan Tan
2023-08-01 18:41 ` [PATCH v7 4/7] t/helper/test-read-graph: implement `bloom-filters` mode Jonathan Tan
2023-08-01 18:41 ` [PATCH v7 5/7] t4216: test changed path filters with high bit paths Jonathan Tan
2023-08-01 18:41 ` [PATCH v7 6/7] repo-settings: introduce commitgraph.changedPathsVersion Jonathan Tan
2023-08-01 18:41 ` [PATCH v7 7/7] commit-graph: new filter ver. that fixes murmur3 Jonathan Tan
2023-08-01 18:44 ` [PATCH v7 0/7] Changed path filter hash fix and version bump Junio C Hamano
2023-08-01 20:58 ` Taylor Blau
2023-08-01 21:07 ` Junio C Hamano
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