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https://issues.apache.org/jira/browse/SPARK-18637?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15706905#comment-15706905
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Zhan Zhang commented on SPARK-18637:
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Here is the comments from UDFType
/**
* If a UDF stores state based on the sequence of records it has processed, it
* is stateful. A stateful UDF cannot be used in certain expressions such as
* case statement and certain optimizations such as AND/OR short circuiting
* don't apply for such UDFs, as they need to be invoked for each record.
* row_sequence is an example of stateful UDF. A stateful UDF is considered to
* be non-deterministic, irrespective of what deterministic() returns.
*
* @return true
*/
boolean stateful() default false;
> Stateful UDF should be considered as nondeterministic
> -----------------------------------------------------
>
> Key: SPARK-18637
> URL: https://issues.apache.org/jira/browse/SPARK-18637
> Project: Spark
> Issue Type: Bug
> Reporter: Zhan Zhang
>
> If the annotation UDFType of a udf is stateful, it shoudl be considered as
> non-deterministic. Otherwise, the catalyst may optimize the plan and return
> the wrong result.
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