[FLINK-40541][table-planner] Detect build-side watermark hidden by column expansion in LATERAL SNAPSHOT - #29081
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…lumn expansion in LATERAL SNAPSHOT LATERAL SNAPSHOT detected the build-side watermark by looking for a row-time indicator field in the projected TABLE argument. When the watermark sits on a column that the column-expansion strategy hides from SELECT * (e.g. a virtual metadata column under EXCLUDE_DEFAULT_VIRTUAL_METADATA_COLUMNS), TABLE t expands to a projection that drops the row-time attribute, so the rule found none and wrongly rejected the query with "LATERAL SNAPSHOT requires a watermark on the build-side input". Recover the row-time attribute from below the hiding projection and re-append it so it reaches the operator: from a WatermarkAssigner, or, when the watermark was pushed into the source, by re-stamping the scan's row-time column (resolved by name from the watermark spec) as a row-time indicator. The top-level Calc projects the re-appended column away, so the output is unchanged. Co-Generated: Claude Opus 4.8 (1M context)
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snuyanzin
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Sep 3, 2026
| + "load_completed_time => CAST(TIMESTAMP '2026-07-01 00:00:00' AS TIMESTAMP_LTZ(3))" | ||
| + ") AS s ON probe.pk = s.bk"; | ||
| final String plan = util.tableEnv().explainSql(sql); | ||
| assertThat(plan).contains("LateralSnapshotJoin"); |
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how about verifying the whole plan instead?
e.g. util.verifyRelPlan
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Closing this PR, opening one with a different approach |
fhueske
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September 3, 2026 20:33
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What is the purpose of the change
LATERAL SNAPSHOT detected the build-side watermark by looking for a row-time indicator field in the projected TABLE argument. When the watermark sits on a column that the column-expansion strategy hides from SELECT * (e.g. a virtual metadata column under EXCLUDE_DEFAULT_VIRTUAL_METADATA_COLUMNS), TABLE t expands to a projection that drops the row-time attribute, so the rule found none and wrongly rejected the query with "LATERAL SNAPSHOT requires a watermark on the build-side input".
Recover the row-time attribute from below the hiding projection and re-append it so it reaches the operator: from a WatermarkAssigner, or, when the watermark was pushed into the source, by re-stamping the scan's row-time column (resolved by name from the watermark spec) as a row-time indicator. The top-level Calc projects the re-appended column away, so the output is unchanged.
Brief change log
Verifying this change
Run new and existing tests for LateralSnapshotJoin
Does this pull request potentially affect one of the following parts:
@Public(Evolving): noDocumentation
Was generative AI tooling used to co-author this PR?
Generated-by: Claude Opus 4.8 (1M context)