wypoon commented on a change in pull request #31451:
URL: https://github.com/apache/spark/pull/31451#discussion_r605096457
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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:
My interest is in the batch scan use case. It is true that, under the
hood, a particular DS v2 may well need to track some particular metric per row,
but there are definitely cases where a metric does not need to be updated per
row; in those cases, simply reporting the metric value at the end of the read
would be cheaper.
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