HeartSaVioR commented on code in PR #39931:
URL: https://github.com/apache/spark/pull/39931#discussion_r1119407026
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sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/statefulOperators.scala:
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@@ -96,6 +98,25 @@ trait StateStoreReader extends StatefulOperator {
/** An operator that writes to a StateStore. */
trait StateStoreWriter extends StatefulOperator with PythonSQLMetrics { self:
SparkPlan =>
+ /**
+ * Produce the output watermark for given input watermark (ms).
+ *
+ * In most cases, this is same as the criteria of state eviction, as most
stateful operators
+ * produce the output from two different kinds:
+ *
+ * 1. without buffering
+ * 2. with buffering (state)
+ *
+ * The state eviction happens when event time exceeds a "certain threshold
of timestamp", which
+ * denotes a lower bound of event time values for output (output watermark).
+ *
+ * The default implementation provides the input watermark as it is. Most
built-in operators
+ * will evict based on min input watermark and ensure it will be minimum of
the event time value
+ * for the output so far (including output from eviction). Operators which
behave differently
+ * (e.g. different criteria on eviction) must override this method.
+ */
+ def produceOutputWatermark(inputWatermarkMs: Long): Option[Long] =
Some(inputWatermarkMs)
Review Comment:
Your example is not consistent. If you want to advance watermark "after" you
produce output, both 5 minutes and 10 minutes window operator watermark should
be 0.
Even we provide the output watermark as same as input watermark, it does not
violate the definition of watermark, lower bound of the "output". Advancing
watermark as 3 for 5 minutes window does not break the logic. Further output
will be at least 5, not less than 3, hence the previous advancement of
watermark is never violated. Current watermark logic has been working like this
way.
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