[SPARK-14408][CORE] Changed RDD.treeAggregate to use fold instead of reduce #18198
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What changes were proposed in this pull request?
Previously,
RDD.treeAggregateusedreduceByKeyandreducein its implementation, neither of which technically allows theseq/combOpsto modify and return their first arguments.This PR uses
foldByKeyandfoldinstead and notes thataggregateandtreeAggregateare semantically identical in the Scala doc.Note that this had some test failures by unknown reasons. This was actually fixed in e355460.
The root cause was, the
zeroValuenow becomesAFTAggregatorand it comparestotalCnt(where the value is actually 0). It starts merging one by one and it keeps returningthiswheretotalCntis 0. So, this looks not the bug in the current change.This is now fixed in the commit. So, this should pass the tests.
How was this patch tested?
Test case added in
RDDSuite.Closes #12217