Ingo Bürk created FLINK-23917:
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Summary: Project metadata columns to apply to sources which do not
implement projection pushdown
Key: FLINK-23917
URL: https://issues.apache.org/jira/browse/FLINK-23917
Project: Flink
Issue Type: Improvement
Components: Table SQL / Planner
Reporter: Ingo Bürk
If a source implements SupportsReadingMetadata, but not
SupportsProjectionPushDown, #applyReadableMetadata is always called with all
metadata keys declared in the table's schema. If SupportsProjectionPushDown is
implemented, this is filtered down to only the required metadata keys. This can
be a problem since metadata could be expensive to calculate.
The root cause for this is that the projection happens in
PushProjectIntoTableSourceScanRule which doesn't run for sources which do not
implement projection pushdown. We should add a new separate rule which projects
required metadata keys for the source in this case.
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