eason-yuchen-liu commented on code in PR #59629:
URL: https://github.com/apache/spark/pull/59629#discussion_r4340488373
##########
sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/operators/stateful/join/StreamingSymmetricHashJoinHelper.scala:
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@@ -243,20 +243,32 @@ object StreamingSymmetricHashJoinHelper extends Logging {
JoinStateKeyWatermarkPredicate(
e,
eventTimeWatermarkForEviction.get,
- eventTimeWatermarkForLateEvents)
+ // V4 can skip keys at or below the previous watermark only if
late-input filtering
+ // rejects new rows in that range on this same key. A watermark on
the other input's
+ // equality key can drive eviction even when this input has no
watermark, or has one
+ // on a different column. New rows can then pass late-input
filtering with keys
+ // already eligible for eviction. V4 must scan from the beginning
to find them;
+ // otherwise, outer joins can fail to emit null rows for these
unmatched inputs.
+ eventTimeWatermarkForLateEvents.filter { _ =>
Review Comment:
nit: `filter { _ => ... }` throws away its argument, and the long comment
inside the arg list is hard to follow. Could this be a `val
prevStateKeyWatermark = if (...) eventTimeWatermarkForLateEvents else None`?
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