From: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
To: Han-Wen Nienhuys <hanwen@google.com>
Cc: git@vger.kernel.org, "Junio C Hamano" <gitster@pobox.com>,
"Carlo Marcelo Arenas Belón" <carenas@gmail.com>
Subject: Re: [PATCH v4 27/28] reftable: fixup for new base topic 2/3
Date: Mon, 30 Aug 2021 16:03:42 +0200 [thread overview]
Message-ID: <87lf4jxbxn.fsf@evledraar.gmail.com> (raw)
In-Reply-To: <CAFQ2z_Pa1fG935rQBQPijE=YHatsHbsLd_f8dT7Zh-grdgwbjg@mail.gmail.com>
On Mon, Aug 30 2021, Han-Wen Nienhuys wrote:
> On Mon, Aug 30, 2021 at 3:22 PM Ævar Arnfjörð Bjarmason
> <avarab@gmail.com> wrote:
>> But we will need at least the optimistic locking of code like
>> builtin/reflog.c wanting to do an expiry, and deciding whether to do
>> that expiry based on a given state of the ref/reflog. I.e. we don't
>> want:
>>
>> 1. Start reflog expiry
>> 2. Code in builtin/reflog.c looks up the OID
>> 3. Code in builtin/reflog.c decides whether expire the reflog
>> 4. Concurrent with #4, another writer updates the ref/reflog pair
>> 5. Code in builtin/reflog.c says "OK, expire it!"
>> 6. Reftable queues a delete/prune of the reflog per #5.
>>
>> This would be a sequente of updates to the ref/reflog, none of whom were
>> racy as far as the reftable semantics itself are concerneb, but where
>> we'd do the wrong thing because the writer thought we had A when we
>> really had B. So we need the equivalent of an "git update-ref" with the
>> "<oldvalue>".
>>
>> Is there a better way to do that in this case that I'm missing?
>
> I spent some more time looking at builtin/reflog.c, but I am still not
> 100% sure what the locking is used for.
>
> From a quick glance, the OID goes into tip_commit, and tip_commit goes
> into a reachable list (?). The reachable list is then for something,
> but I can't really tell what.
>
> In your example with 1.-6., it's still not clear to me what the
> undesired behavior is precisely. If the reflog is pruned in #6, is the
> worry that the update in #4 is pruned immediately after being
> effected?
Yes, I think so. But I'm not sure. I skimmed the code quickly today, and
when I wrote the referenced series didn't focus much on the nitty-gritty
of the builtin/reflog.c behavior other than assuring myself that I was
doing the exact same thing as before as far as its logic was concerned.
I.e. it always locked at a given OID. Before my in-flight "reflog
expire: don't lock reflogs using previously seen OI" it might not lock
but get this error:
error: cannot lock ref '<refname>': ref '<refname>' is at <OID-A> but expected <OID-B>
But at least it wouldn't do anything, but the current code does require
the passed-in OID. See the code that needs "unreachable_expire_kind" and
"tip_commit".
Perhaps that whole thing can also be refactored somehow. If I change the
"commit = lookup_commit(the_repository, oid);" in
"reflog_expiry_prepare()" to just "commit = NULL" all tests pass, but
that might just be missing test coverage in the face of same race...
next prev parent reply other threads:[~2021-08-30 14:08 UTC|newest]
Thread overview: 132+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-20 17:04 [PATCH 00/26] Support reftable ref backend for Git Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 01/26] hash.h: provide constants for the hash IDs Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 02/26] init-db: set the_repository->hash_algo early on Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 03/26] reftable: RFC: add LICENSE Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 04/26] reftable: add error related functionality Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 05/26] reftable: utility functions Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 06/26] reftable: add blocksource, an abstraction for random access reads Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 07/26] reftable: (de)serialization for the polymorphic record type Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 08/26] Provide zlib's uncompress2 from compat/zlib-compat.c Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 09/26] reftable: reading/writing blocks Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 10/26] reftable: a generic binary tree implementation Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 11/26] reftable: write reftable files Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 12/26] reftable: generic interface to tables Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 13/26] reftable: read reftable files Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 14/26] reftable: reftable file level tests Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 15/26] reftable: add a heap-based priority queue for reftable records Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 16/26] reftable: add merged table view Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 17/26] reftable: implement refname validation Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 18/26] reftable: implement stack, a mutable database of reftable files Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 19/26] reftable: add dump utility Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 20/26] refs: RFC: Reftable support for git-core Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 21/26] git-prompt: prepare for reftable refs backend SZEDER Gábor via GitGitGadget
2021-07-20 17:04 ` [PATCH 22/26] Add "test-tool dump-reftable" command Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 23/26] t1301: document what needs to be done for reftable Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 24/26] t1401,t2011: parameterize HEAD.lock for REFFILES Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 25/26] t1404: annotate test cases with REFFILES Han-Wen Nienhuys via GitGitGadget
2021-07-20 17:04 ` [PATCH 26/26] t7004: avoid direct filesystem access Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:16 ` [PATCH v2 00/25] Support reftable ref backend for Git Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:16 ` [PATCH v2 01/25] hash.h: provide constants for the hash IDs Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:16 ` [PATCH v2 02/25] init-db: set the_repository->hash_algo early on Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:16 ` [PATCH v2 03/25] reftable: RFC: add LICENSE Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:16 ` [PATCH v2 04/25] reftable: add error related functionality Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:16 ` [PATCH v2 05/25] reftable: utility functions Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:16 ` [PATCH v2 06/25] reftable: add blocksource, an abstraction for random access reads Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:16 ` [PATCH v2 07/25] reftable: (de)serialization for the polymorphic record type Han-Wen Nienhuys via GitGitGadget
2021-08-16 21:54 ` Carlo Marcelo Arenas Belón
2021-08-17 13:44 ` Han-Wen Nienhuys
2021-08-16 20:16 ` [PATCH v2 08/25] Provide zlib's uncompress2 from compat/zlib-compat.c Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:17 ` [PATCH v2 09/25] reftable: reading/writing blocks Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:17 ` [PATCH v2 10/25] reftable: a generic binary tree implementation Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:17 ` [PATCH v2 11/25] reftable: write reftable files Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:17 ` [PATCH v2 12/25] reftable: generic interface to tables Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:17 ` [PATCH v2 13/25] reftable: read reftable files Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:17 ` [PATCH v2 14/25] reftable: reftable file level tests Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:17 ` [PATCH v2 15/25] reftable: add a heap-based priority queue for reftable records Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:17 ` [PATCH v2 16/25] reftable: add merged table view Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:17 ` [PATCH v2 17/25] reftable: implement refname validation Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:17 ` [PATCH v2 18/25] reftable: implement stack, a mutable database of reftable files Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:17 ` [PATCH v2 19/25] reftable: add dump utility Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:17 ` [PATCH v2 20/25] refs: RFC: Reftable support for git-core Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:17 ` [PATCH v2 21/25] git-prompt: prepare for reftable refs backend SZEDER Gábor via GitGitGadget
2021-08-16 20:17 ` [PATCH v2 22/25] Add "test-tool dump-reftable" command Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:17 ` [PATCH v2 23/25] t1301: document what needs to be done for reftable Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:17 ` [PATCH v2 24/25] t1401,t2011: parameterize HEAD.lock for REFFILES Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:17 ` [PATCH v2 25/25] t1404: annotate test cases with REFFILES Han-Wen Nienhuys via GitGitGadget
2021-08-16 20:48 ` [PATCH v2 00/25] Support reftable ref backend for Git Junio C Hamano
2021-08-17 16:38 ` Han-Wen Nienhuys
2021-08-17 13:39 ` [PATCH v3 " Han-Wen Nienhuys via GitGitGadget
2021-08-17 13:39 ` [PATCH v3 01/25] hash.h: provide constants for the hash IDs Han-Wen Nienhuys via GitGitGadget
2021-08-23 9:47 ` Ævar Arnfjörð Bjarmason
2021-08-17 13:39 ` [PATCH v3 02/25] init-db: set the_repository->hash_algo early on Han-Wen Nienhuys via GitGitGadget
2021-08-17 13:39 ` [PATCH v3 03/25] reftable: RFC: add LICENSE Han-Wen Nienhuys via GitGitGadget
2021-08-17 13:39 ` [PATCH v3 04/25] reftable: add error related functionality Han-Wen Nienhuys via GitGitGadget
2021-08-17 13:39 ` [PATCH v3 05/25] reftable: utility functions Han-Wen Nienhuys via GitGitGadget
2021-08-17 13:39 ` [PATCH v3 06/25] reftable: add blocksource, an abstraction for random access reads Han-Wen Nienhuys via GitGitGadget
2021-08-17 13:39 ` [PATCH v3 07/25] reftable: (de)serialization for the polymorphic record type Han-Wen Nienhuys via GitGitGadget
2021-08-17 13:39 ` [PATCH v3 08/25] Provide zlib's uncompress2 from compat/zlib-compat.c Han-Wen Nienhuys via GitGitGadget
2021-08-18 10:14 ` Philip Oakley
2021-08-18 10:39 ` Han-Wen Nienhuys
2021-08-18 11:53 ` Philip Oakley
2021-08-17 13:39 ` [PATCH v3 09/25] reftable: reading/writing blocks Han-Wen Nienhuys via GitGitGadget
2021-08-17 13:39 ` [PATCH v3 10/25] reftable: a generic binary tree implementation Han-Wen Nienhuys via GitGitGadget
2021-08-17 13:39 ` [PATCH v3 11/25] reftable: write reftable files Han-Wen Nienhuys via GitGitGadget
2021-08-17 13:39 ` [PATCH v3 12/25] reftable: generic interface to tables Han-Wen Nienhuys via GitGitGadget
2021-08-17 13:39 ` [PATCH v3 13/25] reftable: read reftable files Han-Wen Nienhuys via GitGitGadget
2021-08-17 13:39 ` [PATCH v3 14/25] reftable: reftable file level tests Han-Wen Nienhuys via GitGitGadget
2021-08-17 13:39 ` [PATCH v3 15/25] reftable: add a heap-based priority queue for reftable records Han-Wen Nienhuys via GitGitGadget
2021-08-17 13:39 ` [PATCH v3 16/25] reftable: add merged table view Han-Wen Nienhuys via GitGitGadget
2021-08-17 13:39 ` [PATCH v3 17/25] reftable: implement refname validation Han-Wen Nienhuys via GitGitGadget
2021-08-17 13:40 ` [PATCH v3 18/25] reftable: implement stack, a mutable database of reftable files Han-Wen Nienhuys via GitGitGadget
2021-08-17 13:40 ` [PATCH v3 19/25] reftable: add dump utility Han-Wen Nienhuys via GitGitGadget
2021-08-17 13:40 ` [PATCH v3 20/25] refs: RFC: Reftable support for git-core Han-Wen Nienhuys via GitGitGadget
2021-08-23 9:50 ` Ævar Arnfjörð Bjarmason
2021-08-30 13:31 ` Han-Wen Nienhuys
2021-08-30 14:10 ` Ævar Arnfjörð Bjarmason
2021-08-17 13:40 ` [PATCH v3 21/25] git-prompt: prepare for reftable refs backend SZEDER Gábor via GitGitGadget
2021-08-17 13:40 ` [PATCH v3 22/25] Add "test-tool dump-reftable" command Han-Wen Nienhuys via GitGitGadget
2021-08-17 13:40 ` [PATCH v3 23/25] t1301: document what needs to be done for reftable Han-Wen Nienhuys via GitGitGadget
2021-08-17 13:40 ` [PATCH v3 24/25] t1401,t2011: parameterize HEAD.lock for REFFILES Han-Wen Nienhuys via GitGitGadget
2021-08-17 13:40 ` [PATCH v3 25/25] t1404: annotate test cases with REFFILES Han-Wen Nienhuys via GitGitGadget
2021-08-23 9:08 ` [PATCH v3 00/25] Support reftable ref backend for Git Ævar Arnfjörð Bjarmason
2021-08-26 16:02 ` Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 00/28] " Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 01/28] hash.h: provide constants for the hash IDs Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 02/28] init-db: set the_repository->hash_algo early on Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 03/28] reftable: RFC: add LICENSE Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 04/28] reftable: add error related functionality Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 05/28] reftable: utility functions Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 06/28] reftable: add blocksource, an abstraction for random access reads Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 07/28] reftable: (de)serialization for the polymorphic record type Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 08/28] Provide zlib's uncompress2 from compat/zlib-compat.c Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 09/28] reftable: reading/writing blocks Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 10/28] reftable: a generic binary tree implementation Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 11/28] reftable: write reftable files Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 12/28] reftable: generic interface to tables Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 13/28] reftable: read reftable files Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 14/28] reftable: reftable file level tests Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 15/28] reftable: add a heap-based priority queue for reftable records Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 16/28] reftable: add merged table view Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 17/28] reftable: implement refname validation Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 18/28] reftable: implement stack, a mutable database of reftable files Ævar Arnfjörð Bjarmason
2021-08-27 5:33 ` Junio C Hamano
2021-08-27 6:01 ` [RFC PATCH] reftable: fixup for broken __FUNCTION__ use Ævar Arnfjörð Bjarmason
2021-08-27 7:00 ` Carlo Arenas
2021-08-30 12:11 ` Han-Wen Nienhuys
2021-08-23 12:12 ` [PATCH v4 19/28] reftable: add dump utility Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 20/28] refs: RFC: Reftable support for git-core Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 21/28] git-prompt: prepare for reftable refs backend Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 22/28] Add "test-tool dump-reftable" command Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 23/28] t1301: document what needs to be done for reftable Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 24/28] t1401,t2011: parameterize HEAD.lock for REFFILES Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 25/28] t1404: annotate test cases with REFFILES Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 26/28] reftable: fixup for new base topic 1/3 Ævar Arnfjörð Bjarmason
2021-08-23 12:12 ` [PATCH v4 27/28] reftable: fixup for new base topic 2/3 Ævar Arnfjörð Bjarmason
2021-08-30 12:32 ` Han-Wen Nienhuys
2021-08-30 13:01 ` Ævar Arnfjörð Bjarmason
2021-08-30 13:48 ` Han-Wen Nienhuys
2021-08-30 14:03 ` Ævar Arnfjörð Bjarmason [this message]
2021-08-23 12:12 ` [PATCH v4 28/28] reftable: fixup for new base topic 3/3 Ævar Arnfjörð Bjarmason
2021-08-26 8:39 ` [PATCH v4 00/28] Support reftable ref backend for Git Junio C Hamano
2021-08-26 8:56 ` Han-Wen Nienhuys
2021-08-26 15:05 ` Junio C Hamano
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