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https://issues.apache.org/jira/browse/FLINK-39481?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18092303#comment-18092303
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Rui Fan commented on FLINK-39481:
---------------------------------
[^WindowDistinctAggregateITCase.testCumulateWindow_Rollup_SplitDistinct-true_ROCKSDB.FAILED.log]
The log from failed case
org.apache.flink.table.planner.runtime.stream.sql.WindowDistinctAggregateITCase.testCumulateWindow_Rollup[SplitDistinct=true,
StateBackend=ROCKSDB] is running.
:
[https://dev.azure.com/apache-flink/apache-flink/_build/results?buildId=76144&view=logs&j=ce3801ad-3bd5-5f06-d165-34d37e757d90&t=3c7de195-40a6-5a8e-de70-3d7aa4749237&l=10667]
{code:java}
Randomly selected true for execution.checkpointing.unaligned.enabled
Randomly selected true for
execution.checkpointing.unaligned.recover-output-on-downstream.enabled
Randomly selected false for execution.checkpointing.during-recovery.enabled
Randomly selected PT0S for execution.checkpointing.aligned-checkpoint-timeout
Randomly selected true for execution.checkpointing.cleaner.parallel-mode
Randomly selected true for
execution.checkpointing.unaligned.interruptible-timers.enabled
Randomly selected true for execution.checkpointing.snapshot-compression
Randomly selected true for execution.checkpointing.file-merging.enabled
Randomly selected true for state.backend.rocksdb.use-ingest-db-restore-mode
Randomly selected 2 for pipeline.watermark-alignment.buffer-size
Randomly selected 2 for table.exec.unbounded-over.version
Randomly selected MAP for table.exec.sink.upsert-materialize-strategy.type
{code}
> [tests] Fix flaky
> WindowDistinctAggregateITCase#testCumulateWindow_GroupingSets
> ----------------------------------------------------------------------------------
>
> Key: FLINK-39481
> URL: https://issues.apache.org/jira/browse/FLINK-39481
> Project: Flink
> Issue Type: Bug
> Components: Table SQL / Planner
> Reporter: featzhang
> Priority: Critical
> Labels: pull-request-available, test-stability
> Attachments:
> WindowDistinctAggregateITCase.testCumulateWindow_Rollup_SplitDistinct-true_ROCKSDB.FAILED.log
>
>
> The test `WindowDistinctAggregateITCase#testCumulateWindow_GroupingSets` is
> flaky
> and fails intermittently in CI due to a race condition in the test framework
> itself.
> 1. Failure Evidence
> Azure Build #74194 (2026-04-17):
> - Run 1: PASS
> - Run 2: PASS
> - Run 3: FAIL ← flaky
> - Run 4: PASS
> Error message:
> org.opentest4j.AssertionFailedError:
> Expected 23 rows but got 14 rows.
> Missing rows (all related to window [2020-10-10T00:00:30, ...]):
> - 0,b,2020-10-10T00:00:30,2020-10-10T00:00:35,1,3.33,3.0,3.0,1
> - 0,b,2020-10-10T00:00:30,2020-10-10T00:00:40,1,3.33,3.0,3.0,1
> - 0,b,2020-10-10T00:00:30,2020-10-10T00:00:45,1,3.33,3.0,3.0,1
> - 0,null,2020-10-10T00:00:30,2020-10-10T00:00:35,1,7.77,7.0,7.0,0
> - 0,null,2020-10-10T00:00:30,2020-10-10T00:00:40,1,7.77,7.0,7.0,0
> - 0,null,2020-10-10T00:00:30,2020-10-10T00:00:45,1,7.77,7.0,7.0,0
> - 1,null,2020-10-10T00:00:30,2020-10-10T00:00:35,2,11.10,7.0,3.0,1
> - 1,null,2020-10-10T00:00:30,2020-10-10T00:00:40,2,11.10,7.0,3.0,1
> - 1,null,2020-10-10T00:00:30,2020-10-10T00:00:45,2,11.10,7.0,3.0,1
> 2. Root Cause Analysis
> The test uses `FailingCollectionSource` with `'failing-source' = 'true'`,
> which intentionally throws an artificial exception to trigger
> checkpoint-restore path.
> The source emits 11 rows with an event at timestamp `2020-10-10 00:00:32` and
> `2020-10-10 00:00:34` at the end of the dataset.
> The flakiness stems from a race condition in `FailingCollectionSource`:
> 1. The source uses a checkpoint-triggered failure mechanism. When the failure
> occurs, only the rows emitted BEFORE the checkpoint are guaranteed to be
> replayed after restore.
> 2. The last 2 rows (timestamps 00:00:32 and 00:00:34) advance the watermark
> past
> `00:00:31`, triggering the cumulate windows ending at 00:00:35/40/45.
> If the failure and restore happen AFTER the source emits rows
> at 00:00:32/00:00:34 but BEFORE the downstream operators flush their state,
> those late-window results can be lost.
> 3. Specifically, the issue is that `FailingCollectionSource` uses a legacy
> `SourceFunction` API with `ctx.getCheckpointLock()`. The timing of when
> `numSuccessfulCheckpoints >= 1 && lastCheckpointedEmittedNum >= 1`
> is satisfied relative to when the last 2 rows are emitted is
> non-deterministic,
> meaning sometimes the last 2 rows are emitted before the artificial failure
> is
> triggered (correct case), and sometimes after (data loss case).
>
> 3. Impact
> - Flink CI blocked intermittently on the `test_ci table` job
> - 3 out of 4 retry runs pass, demonstrating it's a classic flaky test pattern
> - Affects: WindowDistinctAggregateITCase (CUMULATE window with GROUPING
> SETS/CUBE/ROLLUP)
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