rangadi commented on code in PR #39931:
URL: https://github.com/apache/spark/pull/39931#discussion_r1120674821
##########
sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/statefulOperators.scala:
##########
@@ -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
Review Comment:
If the above is correct, I would like to propose an explicit contract
written down in the doc comment for this method:
_An operator guarantees that it will not emit record with an event timestamp
lower than its output watermark_.
It might be obvious, but I think it is better to explicitly state it. cc:
@jerrypeng
##########
sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/statefulOperators.scala:
##########
@@ -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
Review Comment:
Making sure my understanding is correct : As a concrete example: If windowed
aggregation (say `count(over 5 minutes`) emits a record X, it's
'Event-timestamp' is 'window-end'. With this, the stateful operator for count()
can guarantee that it will not any record in the future with lower timestamp
than its output watermark. Is that correct?
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