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

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

All Implemented Interfaces:

GenericUDAFResolver, GenericUDAFResolver2

public class GenericUDAFPercentileApprox
extends AbstractGenericUDAFResolver

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(GenericUDAFParameterInfo info) 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

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

Constructor Detail

GenericUDAFPercentileApprox

public GenericUDAFPercentileApprox()

Method Detail

getEvaluator

public GenericUDAFEvaluator getEvaluator(GenericUDAFParameterInfo info)
                                  throws SemanticException

Description copied from interface: GenericUDAFResolver2

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 GenericUDAFResolver2

Overrides:

getEvaluator in class AbstractGenericUDAFResolver

Parameters:

info - The parameter information that is applicable to the UDAF being invoked.

Throws:

SemanticException