Airblader commented on a change in pull request #16984:
URL: https://github.com/apache/flink/pull/16984#discussion_r695731838
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File path:
flink-table/flink-table-common/src/main/java/org/apache/flink/table/connector/source/abilities/SupportsReadingMetadata.java
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@@ -128,4 +128,19 @@
* @see DecodingFormat#applyReadableMetadata(List)
*/
void applyReadableMetadata(List<String> metadataKeys, DataType
producedDataType);
+
+ /**
+ * Defines whether projections can be applied to metadata columns.
+ *
+ * <p>This method is only called if the source does <em>not</em> implement
{@link
+ * SupportsProjectionPushDown}. In this case, by default the planner will
apply all metadata
+ * declared in a table's schema. By returning {@code true} instead the
source can inform the
+ * planner that it should only apply metadata columns which have actually
been selected.
+ *
+ * <p>If the source implements {@link SupportsProjectionPushDown},
projections of metadata
+ * columns are always considered before calling {@link
#applyReadableMetadata(List, DataType)}.
+ */
+ default boolean supportsMetadataProjection() {
+ return false;
Review comment:
Should we consider defaulting to `true` and setting it to `false` in the
(upsert-)kafka connector?
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