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From: Derrick Stolee <stolee@gmail.com>
To: Jonathan Tan <jonathantanmy@google.com>, gitgitgadget@gmail.com
Cc: git@vger.kernel.org, sandals@crustytoothpaste.net,
	steadmon@google.com, jrnieder@gmail.com, peff@peff.net,
	congdanhqx@gmail.com, phillip.wood123@gmail.com,
	emilyshaffer@google.com, sluongng@gmail.com,
	derrickstolee@github.com, dstolee@microsoft.com
Subject: Re: [PATCH v2 05/11] maintenance: add commit-graph task
Date: Wed, 19 Aug 2020 11:04:55 -0400	[thread overview]
Message-ID: <66ae9121-80c9-4030-1119-a11eab8d392b@gmail.com> (raw)
In-Reply-To: <20200818235126.2836309-1-jonathantanmy@google.com>

On 8/18/2020 7:51 PM, Jonathan Tan wrote:
>> By using 'git commit-graph verify --shallow' we can ensure that
>> the file we just wrote is valid. This is an extra safety precaution
>> that is faster than our 'write' subcommand. In the rare situation
>> that the newest layer of the commit-graph is corrupt, we can "fix"
>> the corruption by deleting the commit-graph-chain file and rewrite
>> the full commit-graph as a new one-layer commit graph. This does
>> not completely prevent _that_ file from being corrupt, but it does
>> recompute the commit-graph by parsing commits from the object
>> database. In our use of this step in Scalar and VFS for Git, we
>> have only seen this issue arise because our microsoft/git fork
>> reverted 43d3561 ("commit-graph write: don't die if the existing
>> graph is corrupt" 2019-03-25) for a while to keep commit-graph
>> writes very fast. We dropped the revert when updating to v2.23.0.
>> The verify still has potential for catching corrupt data across
>> the layer boundary: if the new file has commit X with parent Y
>> in an old file but the commit ID for Y in the old file had a
>> bitswap, then we will notice that in the 'verify' command.
> 
> I'm concerned about having this extra precaution, because it is never
> tested (neither here or in a future patch). When you saw this issue
> arise, was there ever an instance in which a valid set of commit graph
> files turned invalid after this maintenance step? (It seems from your
> description that the set was invalid to begin with, so the maintenance
> step did not fix it but also did not make it worse. And it does not make
> it worse, that seems not too bad to me.)

The cases we've seen this happen were root-caused to hardware
problems (disk or RAM), and the invalid data was present immediately
after the "git commit-graph write" command. Since implementing the
"verify" step after each write, we have not had any user reports of
problems with these files.

Are you suggesting one of these options?

 1. Remove this validation and rewrite entirely.

 2. Remove the rewrite and only delete the known-bad data.

 3. Insert a way to cause the verify to return failure mid-process,
    so that this function can be covered by tests.

Thanks,
-Stolee

  reply	other threads:[~2020-08-19 15:05 UTC|newest]

Thread overview: 91+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-06 15:48 [PATCH 00/11] Maintenance I: Command, gc and commit-graph tasks Derrick Stolee via GitGitGadget
2020-08-06 15:48 ` [PATCH 01/11] maintenance: create basic maintenance runner Derrick Stolee via GitGitGadget
2020-08-07 22:16   ` Martin Ågren
2020-08-12 21:03   ` Jonathan Nieder
2020-08-12 22:07     ` Junio C Hamano
2020-08-12 22:50       ` Jonathan Nieder
2020-08-14  1:05     ` Derrick Stolee
2020-08-06 15:48 ` [PATCH 02/11] maintenance: add --quiet option Derrick Stolee via GitGitGadget
2020-08-06 15:48 ` [PATCH 03/11] maintenance: replace run_auto_gc() Derrick Stolee via GitGitGadget
2020-08-06 15:48 ` [PATCH 04/11] maintenance: initialize task array Derrick Stolee via GitGitGadget
2020-08-06 15:48 ` [PATCH 05/11] maintenance: add commit-graph task Derrick Stolee via GitGitGadget
2020-08-07 22:29   ` Martin Ågren
2020-08-12 13:30     ` Derrick Stolee
2020-08-14 12:23       ` Martin Ågren
2020-08-06 15:48 ` [PATCH 06/11] maintenance: add --task option Derrick Stolee via GitGitGadget
2020-08-06 15:48 ` [PATCH 07/11] maintenance: take a lock on the objects directory Derrick Stolee via GitGitGadget
2020-08-06 15:48 ` [PATCH 08/11] maintenance: create maintenance.<task>.enabled config Derrick Stolee via GitGitGadget
2020-08-06 15:48 ` [PATCH 09/11] maintenance: use pointers to check --auto Derrick Stolee via GitGitGadget
2020-08-06 15:48 ` [PATCH 10/11] maintenance: add auto condition for commit-graph task Derrick Stolee via GitGitGadget
2020-08-06 15:48 ` [PATCH 11/11] maintenance: add trace2 regions for task execution Derrick Stolee via GitGitGadget
2020-08-18 14:22 ` [PATCH v2 00/11] Maintenance I: Command, gc and commit-graph tasks Derrick Stolee via GitGitGadget
2020-08-18 14:22   ` [PATCH v2 01/11] maintenance: create basic maintenance runner Derrick Stolee via GitGitGadget
2020-08-18 14:22   ` [PATCH v2 02/11] maintenance: add --quiet option Derrick Stolee via GitGitGadget
2020-08-18 14:23   ` [PATCH v2 03/11] maintenance: replace run_auto_gc() Derrick Stolee via GitGitGadget
2020-08-18 14:23   ` [PATCH v2 04/11] maintenance: initialize task array Derrick Stolee via GitGitGadget
2020-08-18 23:46     ` Jonathan Tan
2020-08-18 14:23   ` [PATCH v2 05/11] maintenance: add commit-graph task Derrick Stolee via GitGitGadget
2020-08-18 23:51     ` Jonathan Tan
2020-08-19 15:04       ` Derrick Stolee [this message]
2020-08-19 17:43         ` Jonathan Tan
2020-08-18 14:23   ` [PATCH v2 06/11] maintenance: add --task option Derrick Stolee via GitGitGadget
2020-08-19  0:00     ` Jonathan Tan
2020-08-19  0:36       ` Junio C Hamano
2020-08-19 15:09         ` Derrick Stolee
2020-08-19 17:35           ` Jonathan Tan
2020-08-18 14:23   ` [PATCH v2 07/11] maintenance: take a lock on the objects directory Derrick Stolee via GitGitGadget
2020-08-19  0:04     ` Jonathan Tan
2020-08-19 15:10       ` Derrick Stolee
2020-08-18 14:23   ` [PATCH v2 08/11] maintenance: create maintenance.<task>.enabled config Derrick Stolee via GitGitGadget
2020-08-18 14:23   ` [PATCH v2 09/11] maintenance: use pointers to check --auto Derrick Stolee via GitGitGadget
2020-08-18 14:23   ` [PATCH v2 10/11] maintenance: add auto condition for commit-graph task Derrick Stolee via GitGitGadget
2020-08-19  0:09     ` Jonathan Tan
2020-08-19 15:15       ` Derrick Stolee
2020-08-18 14:23   ` [PATCH v2 11/11] maintenance: add trace2 regions for task execution Derrick Stolee via GitGitGadget
2020-08-19  0:11     ` Jonathan Tan
2020-08-18 20:18   ` [PATCH v2 00/11] Maintenance I: Command, gc and commit-graph tasks Junio C Hamano
2020-08-19 14:51     ` Derrick Stolee
2020-08-25 18:33   ` [PATCH v3 " Derrick Stolee via GitGitGadget
2020-08-25 18:33     ` [PATCH v3 01/11] maintenance: create basic maintenance runner Derrick Stolee via GitGitGadget
2020-08-25 18:33     ` [PATCH v3 02/11] maintenance: add --quiet option Derrick Stolee via GitGitGadget
2020-08-25 18:33     ` [PATCH v3 03/11] maintenance: replace run_auto_gc() Derrick Stolee via GitGitGadget
2020-08-25 18:33     ` [PATCH v3 04/11] maintenance: initialize task array Derrick Stolee via GitGitGadget
2020-08-25 18:33     ` [PATCH v3 05/11] maintenance: add commit-graph task Derrick Stolee via GitGitGadget
2020-08-25 18:33     ` [PATCH v3 06/11] maintenance: add --task option Derrick Stolee via GitGitGadget
2020-08-25 18:33     ` [PATCH v3 07/11] maintenance: take a lock on the objects directory Derrick Stolee via GitGitGadget
2020-08-26 23:02       ` Jonathan Tan
2020-08-25 18:33     ` [PATCH v3 08/11] maintenance: create maintenance.<task>.enabled config Derrick Stolee via GitGitGadget
2020-08-25 18:33     ` [PATCH v3 09/11] maintenance: use pointers to check --auto Derrick Stolee via GitGitGadget
2020-08-25 18:33     ` [PATCH v3 10/11] maintenance: add auto condition for commit-graph task Derrick Stolee via GitGitGadget
2020-08-26 23:02       ` Jonathan Tan
2020-08-26 23:56         ` Junio C Hamano
2020-08-25 18:33     ` [PATCH v3 11/11] maintenance: add trace2 regions for task execution Derrick Stolee via GitGitGadget
2020-09-04 13:09     ` [PATCH v4 00/11] Maintenance I: Command, gc and commit-graph tasks Derrick Stolee via GitGitGadget
2020-09-04 13:09       ` [PATCH v4 01/11] maintenance: create basic maintenance runner Derrick Stolee via GitGitGadget
2020-09-04 13:09       ` [PATCH v4 02/11] maintenance: add --quiet option Derrick Stolee via GitGitGadget
2020-09-04 13:09       ` [PATCH v4 03/11] maintenance: replace run_auto_gc() Derrick Stolee via GitGitGadget
2020-09-04 13:09       ` [PATCH v4 04/11] maintenance: initialize task array Derrick Stolee via GitGitGadget
2020-09-04 13:09       ` [PATCH v4 05/11] maintenance: add commit-graph task Derrick Stolee via GitGitGadget
2020-09-04 13:09       ` [PATCH v4 06/11] maintenance: add --task option Derrick Stolee via GitGitGadget
2020-09-04 13:09       ` [PATCH v4 07/11] maintenance: take a lock on the objects directory Derrick Stolee via GitGitGadget
2020-09-04 13:09       ` [PATCH v4 08/11] maintenance: create maintenance.<task>.enabled config Derrick Stolee via GitGitGadget
2020-09-04 13:09       ` [PATCH v4 09/11] maintenance: use pointers to check --auto Derrick Stolee via GitGitGadget
2020-09-04 13:09       ` [PATCH v4 10/11] maintenance: add auto condition for commit-graph task Derrick Stolee via GitGitGadget
2020-09-04 13:09       ` [PATCH v4 11/11] maintenance: add trace2 regions for task execution Derrick Stolee via GitGitGadget
2020-09-17 18:11       ` [PATCH v5 00/11] Maintenance I: Command, gc and commit-graph tasks Derrick Stolee via GitGitGadget
2020-09-17 18:11         ` [PATCH v5 01/11] maintenance: create basic maintenance runner Derrick Stolee via GitGitGadget
2020-09-17 18:11         ` [PATCH v5 02/11] maintenance: add --quiet option Derrick Stolee via GitGitGadget
2020-09-17 18:11         ` [PATCH v5 03/11] maintenance: replace run_auto_gc() Derrick Stolee via GitGitGadget
2020-09-17 18:11         ` [PATCH v5 04/11] maintenance: initialize task array Derrick Stolee via GitGitGadget
2020-09-17 18:11         ` [PATCH v5 05/11] maintenance: add commit-graph task Derrick Stolee via GitGitGadget
2020-09-17 18:11         ` [PATCH v5 06/11] maintenance: add --task option Derrick Stolee via GitGitGadget
2020-09-17 18:11         ` [PATCH v5 07/11] maintenance: take a lock on the objects directory Derrick Stolee via GitGitGadget
2020-09-21 13:36           ` Ævar Arnfjörð Bjarmason
2020-09-21 13:43             ` Derrick Stolee
2020-09-21 19:29               ` Junio C Hamano
2020-09-17 18:11         ` [PATCH v5 08/11] maintenance: create maintenance.<task>.enabled config Derrick Stolee via GitGitGadget
2020-09-17 18:11         ` [PATCH v5 09/11] maintenance: use pointers to check --auto Derrick Stolee via GitGitGadget
2020-09-17 18:11         ` [PATCH v5 10/11] maintenance: add auto condition for commit-graph task Derrick Stolee via GitGitGadget
2020-09-17 18:11         ` [PATCH v5 11/11] maintenance: add trace2 regions for task execution Derrick Stolee via GitGitGadget
2020-09-17 18:35         ` [PATCH v5 00/11] Maintenance I: Command, gc and commit-graph tasks Junio C Hamano
2020-09-18 13:14           ` Johannes Schindelin

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