org.apache.hive.builtins
Class UDAFUnionMap

java.lang.Object
  org.apache.hadoop.hive.ql.udf.generic.AbstractGenericUDAFResolver
      org.apache.hive.builtins.UDAFUnionMap

All Implemented Interfaces:

GenericUDAFResolver, GenericUDAFResolver2

public class UDAFUnionMap
extends AbstractGenericUDAFResolver

Aggregate all maps into a single map. If there are multiple values for the same key, result can contain any of those values. Because the mappers must keep all of the data in memory, if your data is non-trivially large you should set hive.map.aggr=false to ensure that UNION_MAP is only executed in the reduce phase.

Nested Class Summary

static class	UDAFUnionMap.Evaluator
static class	UDAFUnionMap.State

Constructor Summary

UDAFUnionMap()

Method Summary

GenericUDAFEvaluator

getEvaluator(TypeInfo[] parameters) Get the evaluator for the parameter types.

Methods inherited from class org.apache.hadoop.hive.ql.udf.generic.AbstractGenericUDAFResolver

getEvaluator

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

UDAFUnionMap

public UDAFUnionMap()

Method Detail

getEvaluator

public GenericUDAFEvaluator getEvaluator(TypeInfo[] parameters)
                                  throws SemanticException

Description copied from interface: GenericUDAFResolver

Get the evaluator for the parameter types. The reason that this function returns an object instead of a class is because it is possible that the object needs some configuration (that can be serialized). In that case the class of the object has to implement the Serializable interface. At execution time, we will deserialize the object from the plan and use it to evaluate the aggregations.

If the class of the object does not implement Serializable, then we will create a new instance of the class at execution time.

Specified by:

getEvaluator in interface GenericUDAFResolver

Overrides:

getEvaluator in class AbstractGenericUDAFResolver

Parameters:

parameters - The types of the parameters. We need the type information to know which evaluator class to use.

Throws:

SemanticException