[jira] [Commented] (FLINK-40115) Document timestamp reliability for bounded-out-of-orderness watermarks

["Paras Mishra (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-40115?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18095207#comment-18095207 ] 

Paras Mishra commented on FLINK-40115:
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Hi [~ipsyer] I’m interested in working on this issue. Could you please assign this ticket to me? Thanks!

> 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
>            Priority: Minor
>
> 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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