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https://issues.apache.org/jira/browse/SPARK-18637?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15706961#comment-15706961
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Zhan Zhang commented on SPARK-18637:
------------------------------------
[~hvanhovell] It is an annotation.
/**
* UDFType annotations are used to describe properties of a UDF. This gives
* important information to the optimizer.
* If the UDF is not deterministic, or if it is stateful, it is necessary to
* annotate it as such for correctness.
*
*/
@Public
@Evolving
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Inherited
public @interface UDFType {
/**
* Certain optimizations should not be applied if UDF is not deterministic.
* Deterministic UDF returns same result each time it is invoked with a
* particular input. This determinism just needs to hold within the context of
* a query.
*
* @return true if the UDF is deterministic
*/
boolean deterministic() default true;
/**
* 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;
/**
* A UDF is considered distinctLike if the UDF can be evaluated on just the
* distinct values of a column. Examples include min and max UDFs. This
* information is used by metadata-only optimizer.
*
* @return true if UDF is distinctLike
*/
boolean distinctLike() default false;
/**
* Using in analytical functions to specify that UDF implies an ordering
*
* @return true if the function implies order
*/
boolean impliesOrder() 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
> Components: SQL
> 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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