cloud-fan commented on a change in pull request #31451:
URL: https://github.com/apache/spark/pull/31451#discussion_r604572473
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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:
Normally, this method should be very cheap, as it just returns the
current metrics values that are being tracked. The implementation may track the
metrics per-row or per-batch, but that's out of our control.
That said, even if we call this method only at the end of partition read,
the perf overhead can still be big if the data source tracks the metrics
per-row under the hood.
@wypoon does it answer your concern?
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