c21 opened a new pull request #30076:
URL: https://github.com/apache/spark/pull/30076
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### What changes were proposed in this pull request?
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This is to support left semi join in stream-stream join. The implementation
of left semi join is (mostly in `StreamingSymmetricHashJoinExec` and
`SymmetricHashJoinStateManager`):
* For left side input row, check if there's a match on right side state
store.
* if there's a match, output the left side row, but do not put the row in
left side state store (no need to put in state store).
* if there's no match, output nothing, but put the row in left side state
store (with "matched" field to set to false in state store).
* For right side input row, check if there's a match on left side state
store.
* For all matched left rows in state store, output the rows with "matched"
field as false. Set all left rows with "matched" field to be true. Only output
the left side rows matched for the first time to guarantee left semi join
semantics.
* State store eviction: evict rows from left/right side state store below
watermark, same as inner join.
Note a followup optimization can be to evict matched left side rows from
state store earlier, even when the rows are still above watermark. However this
needs more change in `SymmetricHashJoinStateManager`, so will leave this as a
followup.
### Why are the changes needed?
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Current stream-stream join supports inner, left outer and right outer join
(https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/StreamingSymmetricHashJoinExec.scala#L166
). We do see internally a lot of users are using left semi stream-stream join
(not spark structured streaming), e.g. I want to get the ad impression (join
left side) which has click (joint right side), but I don't care how many clicks
per ad (left semi semantics).
### Does this PR introduce _any_ user-facing change?
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No.
### How was this patch tested?
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Added unit tests in `UnsupportedOperationChecker.scala` and
`StreamingJoinSuite.scala`.
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