From: Patrick Steinhardt <ps@pks.im>
To: Taylor Blau <me@ttaylorr.com>
Cc: git@vger.kernel.org, Jeff King <peff@peff.net>,
Derrick Stolee <derrickstolee@github.com>,
Junio C Hamano <gitster@pobox.com>
Subject: Re: [PATCH 09/15] refs/packed-backend.c: implement skip lists to avoid excluded pattern(s)
Date: Wed, 10 May 2023 09:25:21 +0200 [thread overview]
Message-ID: <ZFtG4S4XBboztTap@ncase> (raw)
In-Reply-To: <ZFqzW2vqcFJqqPXH@nand.local>
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On Tue, May 09, 2023 at 04:55:55PM -0400, Taylor Blau wrote:
> On Tue, May 09, 2023 at 05:15:43PM +0200, Patrick Steinhardt wrote:
> > On Mon, May 08, 2023 at 06:00:08PM -0400, Taylor Blau wrote:
> >
> > > Note that this optimization is only possible when none of the excluded
> > > pattern(s) have special meta-characters in them. To see why this is the
> > > case, consider the exclusion pattern "refs/foo[a]". In general, in order
> > > to find the location of the first record that matches this pattern, we
> > > could only consider up to the first meta-character, "refs/foo". But this
> > > doesn't work, since the excluded region we'd come up with would include
> > > "refs/foobar", even though it is not excluded.
> >
> > Is this generally true though? A naive implementation would iterate
> > through all references and find the first reference that matches the
> > exclusion regular exepression. From thereon we continue to iterate until
> > we find the first entry that doesn't match. This may cause us to end up
> > with a suboptimal skip list, but the skip list would still be valid.
> >
> > As I said, this implementation would be naive as we're now forced to
> > iterate through all references starting at the beginning. I assume that
> > your implementation will instead use a binary search to locate the first
> > entry that matches the exclusion pattern and the last pattern. But the
> > way this paragraph is formulated makes it sound like this is a general
> > fact, even though it is a fact that derives from the implementation.
> >
> > I of course don't propose to change the algorithm here, but instead to
> > clarify where this restriction actually comes from and why the tradeoff
> > makes sense.
>
> In the example you include, it's possible. But consider something like:
>
> $ git for-each-ref --exclude='refs/foo[ac]'
>
> The region that matches that expression ("refs/fooa", "refs/fooc" and
> everything underneath them) does not have to appear as a continuous
> single region in the packed-refs file. If you have, say, "refs/foobar",
> that will appear between the two regions you want to exclude.
>
> So I think you *might* be able to do it in general, but at the very
> least it would involve splitting each character class and finding the
> start and end of any region(s) that it matches.
>
> Even so, you'd have to try and match each entry as you determine the
> width of the excluded region, at which point you're at par with
> enumerating them anyway and having the caller discard any entries it
> doesn't want.
Alternatively you could also do this on a best-effort basis and only
find the first matching region. But anyway, as said: I'm fine with the
limitations but think that we should document better where they come
from. The current commit message sounds like the limitation is of
general nature even though it is in fact a conciously-chosen tradeoff
that allows us to make the implementation more efficient for most cases.
Patrick
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next prev parent reply other threads:[~2023-05-10 7:25 UTC|newest]
Thread overview: 149+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-08 21:59 [PATCH 00/15] refs: implement skip lists for packed backend Taylor Blau
2023-05-08 21:59 ` [PATCH 01/15] refs.c: rename `ref_filter` Taylor Blau
2023-05-08 21:59 ` [PATCH 02/15] ref-filter.h: provide `REF_FILTER_INIT` Taylor Blau
2023-05-08 21:59 ` [PATCH 03/15] ref-filter: clear reachable list pointers after freeing Taylor Blau
2023-05-08 21:59 ` [PATCH 04/15] ref-filter: add ref_filter_clear() Taylor Blau
2023-05-08 22:29 ` Junio C Hamano
2023-05-08 22:33 ` Taylor Blau
2023-05-09 15:14 ` Patrick Steinhardt
2023-05-09 19:11 ` Taylor Blau
2023-05-08 21:59 ` [PATCH 05/15] ref-filter.c: parameterize match functions over patterns Taylor Blau
2023-05-08 22:36 ` Junio C Hamano
2023-05-09 20:13 ` Taylor Blau
2023-05-08 21:59 ` [PATCH 06/15] builtin/for-each-ref.c: add `--exclude` option Taylor Blau
2023-05-08 23:22 ` Junio C Hamano
2023-05-09 20:22 ` Taylor Blau
2023-05-08 22:00 ` [PATCH 07/15] refs: plumb `exclude_patterns` argument throughout Taylor Blau
2023-05-09 15:14 ` Patrick Steinhardt
2023-05-09 20:23 ` Taylor Blau
2023-05-08 22:00 ` [PATCH 08/15] refs/packed-backend.c: refactor `find_reference_location()` Taylor Blau
2023-05-08 23:56 ` Junio C Hamano
2023-05-09 20:29 ` Taylor Blau
2023-05-08 22:00 ` [PATCH 09/15] refs/packed-backend.c: implement skip lists to avoid excluded pattern(s) Taylor Blau
2023-05-09 0:10 ` Chris Torek
2023-05-09 20:39 ` Taylor Blau
2023-05-09 15:15 ` Patrick Steinhardt
2023-05-09 20:55 ` Taylor Blau
2023-05-09 21:15 ` Taylor Blau
2023-05-10 7:25 ` Patrick Steinhardt [this message]
2023-05-09 23:40 ` Junio C Hamano
2023-05-10 2:30 ` Taylor Blau
2023-05-08 22:00 ` [PATCH 10/15] refs/packed-backend.c: add trace2 counters for skip list Taylor Blau
2023-05-08 22:00 ` [PATCH 11/15] revision.h: store hidden refs in a `strvec` Taylor Blau
2023-05-08 22:00 ` [PATCH 12/15] refs/packed-backend.c: ignore complicated hidden refs rules Taylor Blau
2023-05-08 22:00 ` [PATCH 13/15] refs.h: let `for_each_namespaced_ref()` take excluded patterns Taylor Blau
2023-05-08 22:00 ` [PATCH 14/15] upload-pack.c: avoid enumerating hidden refs where possible Taylor Blau
2023-05-09 15:15 ` Patrick Steinhardt
2023-05-09 21:34 ` Taylor Blau
2023-05-08 22:00 ` [PATCH 15/15] builtin/receive-pack.c: avoid enumerating hidden references Taylor Blau
2023-05-15 19:23 ` [PATCH v2 00/16] refs: implement jump lists for packed backend Taylor Blau
2023-05-15 19:23 ` [PATCH v2 01/16] refs.c: rename `ref_filter` Taylor Blau
2023-05-15 19:23 ` [PATCH v2 02/16] ref-filter.h: provide `REF_FILTER_INIT` Taylor Blau
2023-05-15 19:23 ` [PATCH v2 03/16] ref-filter: clear reachable list pointers after freeing Taylor Blau
2023-05-15 19:23 ` [PATCH v2 04/16] ref-filter: add `ref_filter_clear()` Taylor Blau
2023-05-15 19:23 ` [PATCH v2 05/16] ref-filter.c: parameterize match functions over patterns Taylor Blau
2023-05-15 19:23 ` [PATCH v2 06/16] builtin/for-each-ref.c: add `--exclude` option Taylor Blau
2023-05-15 19:23 ` [PATCH v2 07/16] refs: plumb `exclude_patterns` argument throughout Taylor Blau
2023-05-15 19:23 ` [PATCH v2 08/16] refs/packed-backend.c: refactor `find_reference_location()` Taylor Blau
2023-05-15 19:23 ` [PATCH v2 09/16] refs/packed-backend.c: implement jump lists to avoid excluded pattern(s) Taylor Blau
2023-06-06 7:00 ` Patrick Steinhardt
2023-06-20 12:15 ` Taylor Blau
2023-05-15 19:23 ` [PATCH v2 10/16] refs/packed-backend.c: add trace2 counters for jump list Taylor Blau
2023-05-15 19:23 ` [PATCH v2 11/16] revision.h: store hidden refs in a `strvec` Taylor Blau
2023-06-06 7:00 ` Patrick Steinhardt
2023-06-20 12:16 ` Taylor Blau
2023-05-15 19:23 ` [PATCH v2 12/16] refs/packed-backend.c: ignore complicated hidden refs rules Taylor Blau
2023-05-15 19:23 ` [PATCH v2 13/16] refs.h: let `for_each_namespaced_ref()` take excluded patterns Taylor Blau
2023-06-06 7:01 ` Patrick Steinhardt
2023-06-20 12:18 ` Taylor Blau
2023-05-15 19:23 ` [PATCH v2 14/16] builtin/receive-pack.c: avoid enumerating hidden references Taylor Blau
2023-05-15 19:23 ` [PATCH v2 15/16] upload-pack.c: avoid enumerating hidden refs where possible Taylor Blau
2023-05-15 19:23 ` [PATCH v2 16/16] ls-refs.c: " Taylor Blau
2023-06-06 7:01 ` [PATCH v2 00/16] refs: implement jump lists for packed backend Patrick Steinhardt
2023-06-20 12:22 ` Taylor Blau
2023-06-07 10:40 ` [PATCH v3 " Taylor Blau
2023-06-07 10:40 ` [PATCH v3 01/16] refs.c: rename `ref_filter` Taylor Blau
2023-06-13 22:19 ` Junio C Hamano
2023-06-07 10:40 ` [PATCH v3 02/16] ref-filter.h: provide `REF_FILTER_INIT` Taylor Blau
2023-06-07 10:41 ` [PATCH v3 03/16] ref-filter: clear reachable list pointers after freeing Taylor Blau
2023-06-07 10:41 ` [PATCH v3 04/16] ref-filter: add `ref_filter_clear()` Taylor Blau
2023-06-07 10:41 ` [PATCH v3 05/16] ref-filter.c: parameterize match functions over patterns Taylor Blau
2023-06-13 22:37 ` Junio C Hamano
2023-06-07 10:41 ` [PATCH v3 06/16] builtin/for-each-ref.c: add `--exclude` option Taylor Blau
2023-06-07 10:41 ` [PATCH v3 07/16] refs: plumb `exclude_patterns` argument throughout Taylor Blau
2023-06-13 23:42 ` Junio C Hamano
2023-06-20 11:52 ` Taylor Blau
2023-06-07 10:41 ` [PATCH v3 08/16] refs/packed-backend.c: refactor `find_reference_location()` Taylor Blau
2023-06-07 10:41 ` [PATCH v3 09/16] refs/packed-backend.c: implement jump lists to avoid excluded pattern(s) Taylor Blau
2023-06-14 0:27 ` Junio C Hamano
2023-06-20 12:05 ` Taylor Blau
2023-06-20 18:49 ` Junio C Hamano
2023-06-07 10:41 ` [PATCH v3 10/16] refs/packed-backend.c: add trace2 counters for jump list Taylor Blau
2023-06-14 0:32 ` Junio C Hamano
2023-06-20 12:08 ` Taylor Blau
2023-06-07 10:41 ` [PATCH v3 11/16] revision.h: store hidden refs in a `strvec` Taylor Blau
2023-06-07 10:41 ` [PATCH v3 12/16] refs/packed-backend.c: ignore complicated hidden refs rules Taylor Blau
2023-06-14 0:40 ` Junio C Hamano
2023-06-07 10:41 ` [PATCH v3 13/16] refs.h: let `for_each_namespaced_ref()` take excluded patterns Taylor Blau
2023-06-07 10:42 ` [PATCH v3 14/16] builtin/receive-pack.c: avoid enumerating hidden references Taylor Blau
2023-06-07 10:42 ` [PATCH v3 15/16] upload-pack.c: avoid enumerating hidden refs where possible Taylor Blau
2023-06-07 10:42 ` [PATCH v3 16/16] ls-refs.c: " Taylor Blau
2023-06-12 21:05 ` [PATCH v3 00/16] refs: implement jump lists for packed backend Junio C Hamano
2023-06-20 14:20 ` [PATCH v4 " Taylor Blau
2023-06-20 14:21 ` [PATCH v4 01/16] refs.c: rename `ref_filter` Taylor Blau
2023-07-03 5:13 ` Jeff King
2023-06-20 14:21 ` [PATCH v4 02/16] ref-filter.h: provide `REF_FILTER_INIT` Taylor Blau
2023-07-03 5:15 ` Jeff King
2023-07-03 17:07 ` Taylor Blau
2023-06-20 14:21 ` [PATCH v4 03/16] ref-filter: clear reachable list pointers after freeing Taylor Blau
2023-07-03 5:16 ` Jeff King
2023-06-20 14:21 ` [PATCH v4 04/16] ref-filter: add `ref_filter_clear()` Taylor Blau
2023-07-03 5:19 ` Jeff King
2023-07-03 17:13 ` Taylor Blau
2023-07-03 17:32 ` Jeff King
2023-06-20 14:21 ` [PATCH v4 05/16] ref-filter.c: parameterize match functions over patterns Taylor Blau
2023-07-03 5:27 ` Jeff King
2023-07-03 17:18 ` Taylor Blau
2023-07-03 17:22 ` Taylor Blau
2023-07-03 17:33 ` Jeff King
2023-06-20 14:21 ` [PATCH v4 06/16] builtin/for-each-ref.c: add `--exclude` option Taylor Blau
2023-06-20 14:21 ` [PATCH v4 07/16] refs: plumb `exclude_patterns` argument throughout Taylor Blau
2023-06-20 14:21 ` [PATCH v4 08/16] refs/packed-backend.c: refactor `find_reference_location()` Taylor Blau
2023-06-20 14:21 ` [PATCH v4 09/16] refs/packed-backend.c: implement jump lists to avoid excluded pattern(s) Taylor Blau
2023-07-03 5:56 ` Jeff King
2023-07-03 17:38 ` Taylor Blau
2023-06-20 14:21 ` [PATCH v4 10/16] refs/packed-backend.c: add trace2 counters for jump list Taylor Blau
2023-06-20 14:21 ` [PATCH v4 11/16] revision.h: store hidden refs in a `strvec` Taylor Blau
2023-07-03 5:59 ` Jeff King
2023-06-20 14:22 ` [PATCH v4 12/16] refs/packed-backend.c: ignore complicated hidden refs rules Taylor Blau
2023-07-03 6:18 ` Jeff King
2023-07-04 18:22 ` Taylor Blau
2023-06-20 14:22 ` [PATCH v4 13/16] refs.h: let `for_each_namespaced_ref()` take excluded patterns Taylor Blau
2023-06-20 14:22 ` [PATCH v4 14/16] builtin/receive-pack.c: avoid enumerating hidden references Taylor Blau
2023-06-20 14:22 ` [PATCH v4 15/16] upload-pack.c: avoid enumerating hidden refs where possible Taylor Blau
2023-07-03 6:26 ` Jeff King
2023-07-04 18:43 ` Taylor Blau
2023-06-20 14:22 ` [PATCH v4 16/16] ls-refs.c: " Taylor Blau
2023-07-03 6:27 ` Jeff King
2023-07-03 6:29 ` [PATCH v4 00/16] refs: implement jump lists for packed backend Jeff King
2023-07-10 21:12 ` [PATCH v5 " Taylor Blau
2023-07-10 21:12 ` [PATCH v5 01/16] refs.c: rename `ref_filter` Taylor Blau
2023-07-10 21:12 ` [PATCH v5 02/16] ref-filter.h: provide `REF_FILTER_INIT` Taylor Blau
2023-07-10 21:12 ` [PATCH v5 03/16] ref-filter: clear reachable list pointers after freeing Taylor Blau
2023-07-10 21:12 ` [PATCH v5 04/16] ref-filter: add `ref_filter_clear()` Taylor Blau
2023-07-10 21:12 ` [PATCH v5 05/16] ref-filter.c: parameterize match functions over patterns Taylor Blau
2023-07-10 21:12 ` [PATCH v5 06/16] builtin/for-each-ref.c: add `--exclude` option Taylor Blau
2023-07-10 21:12 ` [PATCH v5 07/16] refs: plumb `exclude_patterns` argument throughout Taylor Blau
2023-07-10 21:12 ` [PATCH v5 08/16] refs/packed-backend.c: refactor `find_reference_location()` Taylor Blau
2023-07-10 21:12 ` [PATCH v5 09/16] refs/packed-backend.c: implement jump lists to avoid excluded pattern(s) Taylor Blau
2023-07-10 21:12 ` [PATCH v5 10/16] refs/packed-backend.c: add trace2 counters for jump list Taylor Blau
2023-07-10 21:12 ` [PATCH v5 11/16] revision.h: store hidden refs in a `strvec` Taylor Blau
2023-07-10 21:12 ` [PATCH v5 12/16] refs.h: let `for_each_namespaced_ref()` take excluded patterns Taylor Blau
2023-07-10 21:12 ` [PATCH v5 13/16] refs.h: implement `hidden_refs_to_excludes()` Taylor Blau
2023-07-10 21:12 ` [PATCH v5 14/16] builtin/receive-pack.c: avoid enumerating hidden references Taylor Blau
2023-07-10 21:12 ` [PATCH v5 15/16] upload-pack.c: avoid enumerating hidden refs where possible Taylor Blau
2023-07-10 21:12 ` [PATCH v5 16/16] ls-refs.c: " Taylor Blau
2023-07-10 22:35 ` [PATCH v5 00/16] refs: implement jump lists for packed backend Junio C Hamano
2023-07-11 9:37 ` Patrick Steinhardt
2023-07-11 15:56 ` Junio C Hamano
2023-07-11 17:19 ` Taylor Blau
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