From: Taylor Blau <me@ttaylorr.com>
To: "SZEDER Gábor" <szeder.dev@gmail.com>
Cc: Taylor Blau <me@ttaylorr.com>,
git@vger.kernel.org, peff@peff.net, dstolee@microsoft.com,
gitster@pobox.com
Subject: Re: [PATCH v3 12/14] commit-graph: add large-filters bitmap chunk
Date: Wed, 2 Sep 2020 16:23:23 -0400 [thread overview]
Message-ID: <20200902202323.GA5281@nand.local> (raw)
In-Reply-To: <20200819133526.GE29528@szeder.dev>
(Finally getting back to this review after working on some other topics
for a while..., sorry for the late response).
On Wed, Aug 19, 2020 at 03:35:26PM +0200, SZEDER Gábor wrote:
> On Tue, Aug 11, 2020 at 04:52:07PM -0400, Taylor Blau wrote:
> > When a commit has more than a certain number of changed paths (commonly
> > 512), the commit-graph machinery represents it as a zero-length filter.
> > This is done since having many entries in the Bloom filter has
> > undesirable effects on the false positivity rate.
>
> This is not the case, the false positive probability depends on the
> ratio of the Bloom filter's size and the number of elements it
> contains, and we size the filters proportional to the number of
> elements they contain, so the number of elements shouldn't affect the
> false positive rate.
I'm not sure that I understand. I agree that the FPR depends on the
ratio between the number of elements in the filter and the filter's
"size". But, consider a Bloom filter that is too small to faithfully
represent all its elements. Such a filter would likely have all its bits
set high, in which case every query would return "maybe", and the FPR
would go up.
> On the contrary, it's the small filters, up to around 30-35 bytes,
> that tend to have larger than expected false positive rate when using
> double hashing.
I agree that small filters suffer from the same, but I think this is an
"in addition" not an "on the contrary".
In either case, I don't think that this is an important detail for the
commit message. What matters is the representation (that we truncate >=
512 elements to a length-zero filter), not why (that can be found in
another commit). I'd have expected to find the rationale in ed591febb4
(bloom.c: core Bloom filter implementation for changed paths.,
2020-03-30), but I couldn't find anything there.
So, I'll drop this sentence entirely to avoid an unimportant detail.
Thanks,
Taylor
next prev parent reply other threads:[~2020-09-02 20:23 UTC|newest]
Thread overview: 117+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-03 18:57 [PATCH 00/10] more miscellaneous Bloom filter improvements Taylor Blau
2020-08-03 18:57 ` [PATCH 01/10] commit-graph: introduce 'get_bloom_filter_settings()' Taylor Blau
2020-08-04 7:24 ` Jeff King
2020-08-04 20:08 ` Taylor Blau
2020-08-03 18:57 ` [PATCH 02/10] commit-graph: pass a 'struct repository *' in more places Taylor Blau
2020-08-03 18:57 ` [PATCH 03/10] t4216: use an '&&'-chain Taylor Blau
2020-08-03 18:57 ` [PATCH 04/10] t/helper/test-read-graph.c: prepare repo settings Taylor Blau
2020-08-03 18:57 ` [PATCH 05/10] commit-graph: respect 'commitgraph.readChangedPaths' Taylor Blau
2020-08-03 18:57 ` [PATCH 06/10] commit-graph.c: sort index into commits list Taylor Blau
2020-08-04 12:31 ` Derrick Stolee
2020-08-04 20:10 ` Taylor Blau
2020-08-03 18:57 ` [PATCH 07/10] commit-graph: add large-filters bitmap chunk Taylor Blau
2020-08-03 18:59 ` Taylor Blau
2020-08-04 12:57 ` Derrick Stolee
2020-08-03 18:57 ` [PATCH 08/10] bloom: split 'get_bloom_filter()' in two Taylor Blau
2020-08-04 13:00 ` Derrick Stolee
2020-08-04 20:12 ` Taylor Blau
2020-08-03 18:57 ` [PATCH 09/10] commit-graph: rename 'split_commit_graph_opts' Taylor Blau
2020-08-03 18:57 ` [PATCH 10/10] builtin/commit-graph.c: introduce '--max-new-filters=<n>' Taylor Blau
2020-08-04 13:03 ` Derrick Stolee
2020-08-04 20:14 ` Taylor Blau
2020-08-05 17:01 ` [PATCH v2 00/14] more miscellaneous Bloom filter improvements Taylor Blau
2020-08-05 17:01 ` [PATCH v2 01/14] commit-graph: introduce 'get_bloom_filter_settings()' Taylor Blau
2020-08-05 17:02 ` [PATCH v2 02/14] t4216: use an '&&'-chain Taylor Blau
2020-08-05 17:02 ` [PATCH v2 03/14] commit-graph: pass a 'struct repository *' in more places Taylor Blau
2020-08-05 17:02 ` [PATCH v2 04/14] t/helper/test-read-graph.c: prepare repo settings Taylor Blau
2020-08-05 17:02 ` [PATCH v2 05/14] commit-graph: respect 'commitGraph.readChangedPaths' Taylor Blau
2020-08-05 17:02 ` [PATCH v2 06/14] commit-graph.c: store maximum changed paths Taylor Blau
2020-08-05 17:02 ` [PATCH v2 07/14] bloom: split 'get_bloom_filter()' in two Taylor Blau
2020-08-05 17:02 ` [PATCH v2 08/14] bloom: use provided 'struct bloom_filter_settings' Taylor Blau
2020-08-05 17:02 ` [PATCH v2 09/14] bloom/diff: properly short-circuit on max_changes Taylor Blau
2020-08-05 17:02 ` [PATCH v2 10/14] commit-graph.c: sort index into commits list Taylor Blau
2020-08-05 17:02 ` [PATCH v2 11/14] csum-file.h: introduce 'hashwrite_be64()' Taylor Blau
2020-08-05 17:02 ` [PATCH v2 12/14] commit-graph: add large-filters bitmap chunk Taylor Blau
2020-08-05 21:01 ` Junio C Hamano
2020-08-05 21:17 ` Taylor Blau
2020-08-05 22:21 ` Junio C Hamano
2020-08-05 22:25 ` Taylor Blau
2020-08-11 13:48 ` Taylor Blau
2020-08-11 18:59 ` Junio C Hamano
2020-08-05 17:03 ` [PATCH v2 13/14] commit-graph: rename 'split_commit_graph_opts' Taylor Blau
2020-08-05 17:03 ` [PATCH v2 14/14] builtin/commit-graph.c: introduce '--max-new-filters=<n>' Taylor Blau
2020-08-11 20:51 ` [PATCH v3 00/14] more miscellaneous Bloom filter improvements Taylor Blau
2020-08-11 20:51 ` [PATCH v3 01/14] commit-graph: introduce 'get_bloom_filter_settings()' Taylor Blau
2020-08-11 21:18 ` SZEDER Gábor
2020-08-11 21:21 ` Taylor Blau
2020-08-11 21:27 ` SZEDER Gábor
2020-08-11 21:34 ` Taylor Blau
2020-08-11 23:55 ` SZEDER Gábor
2020-08-12 11:48 ` Derrick Stolee
2020-08-14 20:17 ` Taylor Blau
2020-08-11 20:51 ` [PATCH v3 02/14] t4216: use an '&&'-chain Taylor Blau
2020-08-11 20:51 ` [PATCH v3 03/14] commit-graph: pass a 'struct repository *' in more places Taylor Blau
2020-08-11 20:51 ` [PATCH v3 04/14] t/helper/test-read-graph.c: prepare repo settings Taylor Blau
2020-08-11 20:51 ` [PATCH v3 05/14] commit-graph: respect 'commitGraph.readChangedPaths' Taylor Blau
2020-08-11 20:51 ` [PATCH v3 06/14] commit-graph.c: store maximum changed paths Taylor Blau
2020-08-11 20:51 ` [PATCH v3 07/14] bloom: split 'get_bloom_filter()' in two Taylor Blau
2020-08-11 20:51 ` [PATCH v3 11/14] csum-file.h: introduce 'hashwrite_be64()' Taylor Blau
2020-08-11 20:51 ` [PATCH v3 08/14] bloom: use provided 'struct bloom_filter_settings' Taylor Blau
2020-08-11 20:51 ` [PATCH v3 09/14] bloom/diff: properly short-circuit on max_changes Taylor Blau
2020-08-11 20:52 ` [PATCH v3 10/14] commit-graph.c: sort index into commits list Taylor Blau
2020-08-11 20:52 ` [PATCH v3 12/14] commit-graph: add large-filters bitmap chunk Taylor Blau
2020-08-11 21:11 ` Derrick Stolee
2020-08-11 21:18 ` Taylor Blau
2020-08-11 22:05 ` Taylor Blau
2020-08-19 13:35 ` SZEDER Gábor
2020-09-02 20:23 ` Taylor Blau [this message]
2020-09-01 14:35 ` SZEDER Gábor
2020-09-02 20:40 ` Taylor Blau
2020-08-11 20:52 ` [PATCH v3 13/14] commit-graph: rename 'split_commit_graph_opts' Taylor Blau
2020-08-19 9:56 ` SZEDER Gábor
2020-09-02 21:02 ` Taylor Blau
2020-08-11 20:52 ` [PATCH v3 14/14] builtin/commit-graph.c: introduce '--max-new-filters=<n>' Taylor Blau
2020-08-12 11:49 ` SZEDER Gábor
2020-08-14 20:20 ` Taylor Blau
2020-08-17 22:50 ` SZEDER Gábor
2020-09-02 21:03 ` Taylor Blau
2020-08-12 12:29 ` Derrick Stolee
2020-08-14 20:10 ` Taylor Blau
2020-08-18 22:23 ` SZEDER Gábor
2020-09-03 16:35 ` Taylor Blau
2020-08-19 8:20 ` SZEDER Gábor
2020-09-03 16:42 ` Taylor Blau
2020-09-04 8:50 ` SZEDER Gábor
2020-09-01 14:36 ` SZEDER Gábor
2020-09-03 18:49 ` Taylor Blau
2020-09-03 21:45 ` [PATCH v3 00/14] more miscellaneous Bloom filter improvements Junio C Hamano
2020-09-03 22:33 ` Taylor Blau
2020-09-03 22:45 ` [PATCH v4 " Taylor Blau
2020-09-03 22:46 ` [PATCH v4 01/14] commit-graph: introduce 'get_bloom_filter_settings()' Taylor Blau
2020-09-03 22:46 ` [PATCH v4 02/14] t4216: use an '&&'-chain Taylor Blau
2020-09-03 22:46 ` [PATCH v4 03/14] commit-graph: pass a 'struct repository *' in more places Taylor Blau
2020-09-03 22:46 ` [PATCH v4 04/14] t/helper/test-read-graph.c: prepare repo settings Taylor Blau
2020-09-03 22:46 ` [PATCH v4 05/14] commit-graph: respect 'commitGraph.readChangedPaths' Taylor Blau
2020-09-03 22:46 ` [PATCH v4 06/14] commit-graph.c: store maximum changed paths Taylor Blau
2020-09-03 22:46 ` [PATCH v4 07/14] bloom: split 'get_bloom_filter()' in two Taylor Blau
2020-09-05 17:22 ` Jakub Narębski
2020-09-05 17:38 ` Taylor Blau
2020-09-05 17:50 ` Jakub Narębski
2020-09-05 18:01 ` Taylor Blau
2020-09-05 18:18 ` Jakub Narębski
2020-09-05 18:38 ` Taylor Blau
2020-09-05 18:55 ` Taylor Blau
2020-09-05 19:04 ` SZEDER Gábor
2020-09-05 19:49 ` Taylor Blau
2020-09-06 21:52 ` Junio C Hamano
2020-09-03 22:46 ` [PATCH v4 08/14] bloom: use provided 'struct bloom_filter_settings' Taylor Blau
2020-09-03 22:46 ` [PATCH v4 09/14] bloom/diff: properly short-circuit on max_changes Taylor Blau
2020-09-03 22:46 ` [PATCH v4 10/14] commit-graph.c: sort index into commits list Taylor Blau
2020-09-03 22:46 ` [PATCH v4 11/14] csum-file.h: introduce 'hashwrite_be64()' Taylor Blau
2020-09-04 20:18 ` René Scharfe
2020-09-04 20:22 ` Taylor Blau
2020-09-03 22:46 ` [PATCH v4 12/14] commit-graph: add large-filters bitmap chunk Taylor Blau
2020-09-03 22:46 ` [PATCH v4 13/14] commit-graph: rename 'split_commit_graph_opts' Taylor Blau
2020-09-04 15:20 ` Taylor Blau
2020-09-03 22:47 ` [PATCH v4 14/14] builtin/commit-graph.c: introduce '--max-new-filters=<n>' Taylor Blau
2020-09-04 14:39 ` [PATCH v4 00/14] more miscellaneous Bloom filter improvements Derrick Stolee
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