[SPARK-38887][SQL] Support switch inner join side for sort merge join #36180
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What changes were proposed in this pull request?
Enhance the selection of
SortMergeJoin
streamed side and buffered side inJoinSelection
, so that we can get a buffered side for better performance.Why are the changes needed?
For an inner join type SortMergeJoin, it always uses the left side as streamed side and right side as buffered side.
Accoirding to the implementaion of SortMergeJoin, we expect the buffered side to be:
We do not know whether the join will be SortMergeJoin at logical phase, so it should do this selection at physcial phase.
For example:
We can make t1 as the buffered side if its statistics size less than t2.
Does this PR introduce any user-facing change?
The plan may be changed and improve the performance.
How was this patch tested?
add test