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https://issues.apache.org/jira/browse/FLINK-40475?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ASF GitHub Bot updated FLINK-40475:
-----------------------------------
Labels: pull-request-available (was: )
> StatusWatermarkValve loses or stalls watermarks when subpartitions realign
> after idleness
> -----------------------------------------------------------------------------------------
>
> Key: FLINK-40475
> URL: https://issues.apache.org/jira/browse/FLINK-40475
> Project: Flink
> Issue Type: Bug
> Components: Runtime / Task
> Reporter: Martijn Visser
> Priority: Critical
> Labels: pull-request-available
>
> When a subpartition of {{StatusWatermarkValve}} reactivates after idleness
> and rejoins the aligned set, the min watermark across aligned subpartitions
> is not re-derived. This breaks the invariant that the aligned min equals the
> last output watermark, which two guards ({{subpartitionStatus.watermark ==
> lastOutputWatermark}}) silently rely on. Two symptoms:
> The all-idle flush-to-max from FLINK-7728 is skipped when the last
> subpartition to become idle is unaligned (went idle, resumed, only partially
> caught up). The final watermark then depends on the order in which inputs
> became idle — the exact defect FLINK-7728 was created to fix. Example: inputs
> at 100/60/70, last output watermark 70; if the input at 60 idles last, the
> valve emits only IDLE and the watermark stays at 70 instead of flushing 100.
> A different idle order emits 100. This also diverges from
> {{CombinedWatermarkStatus}}, which flushes unconditionally since FLINK-38454
> despite the "keep in sync" contract.
> A subpartition that reactivates as the only aligned subpartition has its
> watermark stalled indefinitely — it is only emitted once an even larger
> watermark arrives on that subpartition. No all-idle transition is involved.
> The pattern is reachable with standard sources: {{WatermarkToDataOutput}}
> enforces watermark monotonicity only per subtask and emits ACTIVE before the
> resuming watermark, so e.g. a quiet Kafka partition with
> {{WatermarksWithIdleness}} resuming with old-timestamped backlog reactivates
> below the downstream valve's last output watermark.
> Fix: re-derive the min watermark after realignment on reactivation, and drop
> both guards — {{findAndOutputMaxWatermarkAcrossAllSubpartitions}} and
> {{findAndOutputNewMinWatermarkAcrossAlignedSubpartitions}} already only emit
> on advancement, so monotonicity is unaffected. Unit tests reproducing both
> symptoms (failing on current master) are included in the PR.
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