[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.treeAggregate
usedreduceByKey
andreduce
in its implementation, neither of which technically allows theseq
/combOps
to modify and return their first arguments.This PR uses
foldByKey
andfold
instead and notes thataggregate
andtreeAggregate
are 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
zeroValue
now becomesAFTAggregator
and it comparestotalCnt
(where the value is actually 0). It starts merging one by one and it keeps returningthis
wheretotalCnt
is 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