org.apache.hadoop.hive.ql.udf

Annotation Type UDFType

@InterfaceAudience.Public
@InterfaceStability.Evolving
@Target(value=TYPE)
@Retention(value=RUNTIME)
@Inherited
public @interface UDFType

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.

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element and Description
boolean	deterministic Certain optimizations should not be applied if UDF is not deterministic.
boolean	distinctLike A UDF is considered distinctLike if the UDF can be evaluated on just the distinct values of a column.
boolean	impliesOrder Using in analytical functions to specify that UDF implies an ordering
boolean	stateful If a UDF stores state based on the sequence of records it has processed, it is stateful.

Element Detail

deterministic

public abstract boolean deterministic

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.

Returns:

true if the UDF is deterministic

Default:

true

stateful

public abstract boolean stateful

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.

Returns:

true

Default:

false

distinctLike

public abstract boolean distinctLike

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.

Returns:

true if UDF is distinctLike

Default:

false

impliesOrder

public abstract boolean impliesOrder

Using in analytical functions to specify that UDF implies an ordering

Returns:

true if the function implies order

Default:

false