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Posted to issues@flink.apache.org by "Jelmer Kuperus (JIRA)" <ji...@apache.org> on 2018/03/02 22:28:00 UTC
[jira] [Commented] (FLINK-8467) Restoring job that does not use
checkpointing from savepoint breaks
[ https://issues.apache.org/jira/browse/FLINK-8467?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16384252#comment-16384252 ]
Jelmer Kuperus commented on FLINK-8467:
---------------------------------------
Sorry for the late response. I just realized that notifications go to an old email address.
I understand and agree that when you create a savepoint, the offsets stored in the savepoint should be used after a restore from savepoint
However if you have a job that does not use checkpointing that crashes and is automatically restarted after it was restored from a savepoint. Then it will reprocess all the messages received since the savedpoint Even if this restart where to happen say a year since this job was restored from the savepoint.
In a job that has checkpointing enabled this would not be a problem, because new checkpoints are regularly written to disk. and the restarted job would continue from the last written checkpoint.
The behavior I expected for a job that does not use checkpointing is that on failure it would continue from the offsets stored in kafka. This way if the job would fail a year after it was restored from a savepoint only max _auto.commit.interval.ms_ worth of events would be replayed. Which is exactly how the job would behave had you not restored in from a savepoint.
One could argue that you should then simply not create a savepoint for these jobs. Which will solve the problem. But when you are upgrading flink and that server has many jobs running on it you might not know which jobs do or do not have checkpointing enabled. And if you follow the instructions in the upgrade guide by the letter, then you will inadvertently create serious problems.
> Restoring job that does not use checkpointing from savepoint breaks
> -------------------------------------------------------------------
>
> Key: FLINK-8467
> URL: https://issues.apache.org/jira/browse/FLINK-8467
> Project: Flink
> Issue Type: Bug
> Components: State Backends, Checkpointing
> Reporter: Jelmer Kuperus
> Priority: Major
>
> When checkpointing is disabled, the Flink Kafka Consumer relies on the periodic offsets that are committed to the broker by the internal Kafka client. Such a job would, upon restart, continue from the committed offsets. However, in the situation that the job is restored from a savepoint, then the offsets within the savepoint supercede the broker-based offsets.
> Here's a simple project that demonstrates the problem : [https://github.com/jelmerk/flink-cancel-restart-job-without-checkpointing]
> And a link to the mailing list thread : [http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/Starting-a-job-that-does-not-use-checkpointing-from-a-savepoint-is-broken-td17874.html]
>
> If this is not something you want to address at least the upgrading guide ([https://ci.apache.org/projects/flink/flink-docs-release-1.4/ops/upgrading.html)] should caution against this
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