srowen commented on a change in pull request #24890: [SPARK-28074][DOC][SS]
Document caveats on using multiple stateful operations in single query
URL: https://github.com/apache/spark/pull/24890#discussion_r295031038
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File path: docs/structured-streaming-programming-guide.md
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@@ -3146,6 +3146,17 @@ See [Input Sources](#input-sources) and [Output
Sinks](#output-sinks) sections f
- After `coalesce`, the number of (reduced) tasks will be kept unless
another shuffle happens.
- `spark.sql.streaming.stateStore.providerClass`: To read the previous state
of the query properly, the class of state store provider should be unchanged.
- `spark.sql.streaming.multipleWatermarkPolicy`: Modification of this would
lead inconsistent watermark value when query contains multiple watermarks,
hence the policy should be unchanged.
+- Structured Streaming uses `global watermark` which might impact on query
having multiple stateful operations.
Review comment:
_a_ global watermark? it also shouldn't be code-formatted
impact on query -> impact a query.
How would it impact the query?
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