aokolnychyi commented on code in PR #6304:
URL: https://github.com/apache/iceberg/pull/6304#discussion_r1034126627
##########
api/src/main/java/org/apache/iceberg/ScanTaskGroup.java:
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@@ -26,6 +26,24 @@
* @param <T> the type of scan tasks
*/
public interface ScanTaskGroup<T extends ScanTask> extends ScanTask {
+ /**
+ * Returns a grouping key for this task group.
+ *
+ * <p>Tasks may produce records that belong to a specific group of data
(e.g. partition). It may
+ * be beneficial to preserve that grouping while combining tasks into groups
if query engines can
+ * leverage that information to avoid shuffles. Grouping keys indicate how
data is split between
+ * different task groups. The grouping key type is determined at planning
time and is identical
+ * across all task groups produced by a scan.
+ *
+ * <p>All records produced by tasks in this group are guaranteed to have the
reported grouping
+ * key. Implementations should return an empty struct if the data grouping
is random or unknown.
+ *
+ * @return a grouping key for this task group
+ */
+ default StructLike groupingKey() {
Review Comment:
I also considered calling it `partitionKey`. However, I went for
`groupingKey`:
- It is more generic. We may expose grouping on non-partition attributes in
the future.
- It matches `Partitioning$groupingKeyType`, which is inspired by
`KeyGroupedPartitioning` in Spark.
- It avoids confusion between `partitionKey` and `partition` (reported by
`PartitionScanTask`).
- Calling it `partitionKey` may be misleading as we consider only non-void
transforms.
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