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https://issues.apache.org/jira/browse/FLINK-38345?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18051609#comment-18051609
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Rion Williams commented on FLINK-38345:
---------------------------------------
The related PR that I posed for this was just aged out due to staleness (120
days) without review. I wanted to comment on here to update the ticket to see
if we could re-open the issue for a potential review/merge.
> HybridSource checkpoint recovery results in NPE if addSource depends on
> previousEnumerator from SourceSwitchContext
> -------------------------------------------------------------------------------------------------------------------
>
> Key: FLINK-38345
> URL: https://issues.apache.org/jira/browse/FLINK-38345
> Project: Flink
> Issue Type: Bug
> Components: Connectors / HybridSource
> Affects Versions: 2.0.0, 1.19.1
> Reporter: Matt Cuento
> Priority: Minor
> Labels: pull-request-available
>
> {{org.apache.flink.connector.base.source.hybrid.HybridSource}} upon recovery
> from a checkpoint calls {{restoreEnumerator()}} with the configured source
> factories and checkpoint information.
> The enumerator
> {{org.apache.flink.connector.base.source.hybrid.HybridSourceSplitEnumerator}}
> then is started which invokes {{{}switchEnumerator(){}}}.
> The {{currentEnumerator}} is null on recovery and as part of source switching
> logic, {{previousEnumerator}} becomes null.
> For hybrid source implementations that require the use of the
> {{org.apache.flink.connector.base.source.hybrid.HybridSource.SourceSwitchContext}}
> to derive a start position at switch time, we end up in a situation where
> {{getPreviousEnumerator()}} returns null, meaning we're unable to derive a
> start position on checkpoint recovery.
> Enumerator state is later deserialized and recovered, but requires a source
> to get the serializer needed. So long as a source depends on a prior
> enumerator to derive the start position, this bug will be in effect.
>
> This bug can be reproduced via a unit test in the enumerator [1].
>
> [1] - [https://github.com/apache/flink/pull/26975]
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