Hancheng Deng created FLINK-40115:
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Summary: Document timestamp reliability for
bounded-out-of-orderness watermarks
Key: FLINK-40115
URL: https://issues.apache.org/jira/browse/FLINK-40115
Project: Flink
Issue Type: Improvement
Components: Documentation
Reporter: Hancheng Deng
The documentation page "Generating Watermarks" includes an example of a
bounded-out-of-orderness watermark generator that advances watermarks from the
maximum observed event timestamp.
This behavior is correct and efficient when event timestamps are reliable and
the out-of-orderness bound matches the stream characteristics. However, streams
may contain future timestamps, device clock errors, or backfilled records mixed
with real-time records. In such cases, a single far-ahead timestamp can advance
the watermark too aggressively and make subsequent records appear late.
This issue proposes adding a short documentation note after the
bounded-out-of-orderness watermark generator example to remind users that
timestamps used for watermark generation should be reliable, and to mention
mitigation options such as timestamp validation, a larger out-of-orderness
bound, allowed lateness, late-record side outputs, or a custom
WatermarkGenerator.
This is a documentation-only improvement and does not change Flink behavior.
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