Arvid Heise created FLINK-40926:
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Summary: Projection push down records a ReadingMetadata ability
without metadata keys
Key: FLINK-40926
URL: https://issues.apache.org/jira/browse/FLINK-40926
Project: Flink
Issue Type: Bug
Components: Table SQL / Planner
Affects Versions: 2.4.0
Reporter: Arvid Heise
Assignee: Arvid Heise
For a source that implements SupportsReadingMetadata, the planner records a
ReadingMetadata ability even if the query reads no metadata column:
{code:sql}
CREATE TABLE src (a INT, b BIGINT) WITH ('connector' = 'values');
SELECT a FROM src WHERE b > 1;
{code}
{noformat}
TableSourceScan(table=[[default_catalog, default_database, src, filter=[...],
project=[a], metadata=[]]], fields=[a])
{noformat}
The compiled plan carries the same entry:
{code:json}
{ "type" : "ReadingMetadata", "metadataKeys" : [ ], "producedType" : "ROW<`a`
INT> NOT NULL" }
{code}
The entry is added by PushProjectIntoTableSourceScanRule (similarly in
ScanReuser) whenever the source supports metadata, independent of whether any
metadata key is projected. On restore it results in an applyReadableMetadata
call with an empty key list.
It is unclear whether this entry is needed at all; most restore test plans in
flink-table-planner contain it.
Found while reviewing https://github.com/apache/flink/pull/29385.
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