HeartSaVioR commented on a change in pull request #28975:
URL: https://github.com/apache/spark/pull/28975#discussion_r449297581
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File path:
sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/state/SymmetricHashJoinStateManager.scala
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@@ -451,10 +451,25 @@ class SymmetricHashJoinStateManager(
}
private trait KeyWithIndexToValueRowConverter {
+ /** Defines the schema of the value row (the value side of K-V in state
store). */
def valueAttributes: Seq[Attribute]
+ /**
+ * Convert the value row to (actual value, match) pair.
+ *
+ * NOTE: implementations should ensure the result row is NOT reused during
execution, as
+ * caller may use the value to store without copy().
Review comment:
So the problem occurred here:
https://github.com/apache/spark/blob/42f01e314b4874236544cc8b94bef766269385ee/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/state/SymmetricHashJoinStateManager.scala#L252-L281
Here we temporarily store `currentValue` via calling `convertValue` which is
candidate to remove (and return). After that we adjust the array a bit to not
having a hole in between, where it also triggers `convertValue` and "changes"
the value in `currentValue` silently if we don't copy.
It's also possible for caller to call copy() but the row to copy is inside
of ValueAndMatchPair so I feel it's pretty much easier to miss even with method
doc, so I took safer approach rather than performance-wise.
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