cloud-fan commented on a change in pull request #31451:
URL: https://github.com/apache/spark/pull/31451#discussion_r605374302
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File path:
sql/catalyst/src/main/java/org/apache/spark/sql/connector/read/PartitionReader.java
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@@ -51,7 +51,8 @@
T get();
/**
- * Returns an array of custom task metrics. By default it returns empty
array.
+ * Returns an array of custom task metrics. By default it returns empty
array. Note that it is
+ * not recommended to put heavy logic in this method as it may affect
reading performance.
Review comment:
Since we can't control how frequently the underlying data source tracks
the metrics, this is all about how frequently we want to update the SQL metrics.
Since the actual metrics update is sent to the driver via heartbeat, it's
not very useful if we update the metrics per-row. How about we do it like per
100 rows? Only update once may be problematic if the task runs for a long time.
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