cloud-fan commented on a change in pull request #31476:
URL: https://github.com/apache/spark/pull/31476#discussion_r572298710
##########
File path:
sql/catalyst/src/main/java/org/apache/spark/sql/connector/read/Scan.java
##########
@@ -102,4 +102,13 @@ default MicroBatchStream toMicroBatchStream(String
checkpointLocation) {
default ContinuousStream toContinuousStream(String checkpointLocation) {
throw new UnsupportedOperationException(description() + ": Continuous scan
are not supported");
}
+
+ /**
+ * Returns an array of supported custom metrics with name and description.
+ * By default it returns empty array.
+ */
+ default CustomMetric[] supportedCustomMetrics() {
Review comment:
I don't see how a mixin trait helps avoid breaking change. Removing the
trait later is also a breaking change. Agree with @rdblue that an optional
method is simple and sufficient. Some other features have mixin trait because
they don't have a reasonable default if made into optional methods. Metrics is
OK as we can return empty metrics as the default.
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