org.apache.hadoop.hive.ql.udf.generic
Class GenericUDAFPercentileApprox

java.lang.Object
  extended by org.apache.hadoop.hive.ql.udf.generic.GenericUDAFPercentileApprox
All Implemented Interfaces:
GenericUDAFResolver

public class GenericUDAFPercentileApprox
extends Object
implements GenericUDAFResolver

Computes an approximate percentile (quantile) from an approximate histogram, for very large numbers of rows where the regular percentile() UDAF might run out of memory. The input is a single double value or an array of double values representing the quantiles requested. The output, corresponding to the input, is either an single double value or an array of doubles that are the quantile values.


Nested Class Summary
static class GenericUDAFPercentileApprox.GenericUDAFMultiplePercentileApproxEvaluator
           
static class GenericUDAFPercentileApprox.GenericUDAFPercentileApproxEvaluator
          Construct a histogram using the algorithm described by Ben-Haim and Tom-Tov, and then use it to compute an approximate percentile value.
static class GenericUDAFPercentileApprox.GenericUDAFSinglePercentileApproxEvaluator
           
 
Constructor Summary
GenericUDAFPercentileApprox()
           
 
Method Summary
 GenericUDAFEvaluator getEvaluator(TypeInfo[] parameters)
          Get the evaluator for the parameter types.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

GenericUDAFPercentileApprox

public GenericUDAFPercentileApprox()
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
Parameters:
parameters - The types of the parameters. We need the type information to know which evaluator class to use.
Throws:
SemanticException


Copyright © 2011 The Apache Software Foundation