io.crate.execution.engine.aggregation

Class AggregationFunction<TPartial,TFinal>

java.lang.Object

io.crate.execution.engine.aggregation.AggregationFunction<TPartial,TFinal>

Type Parameters:

TPartial - the intermediate type of the value used during aggregation

TFinal - the final type of the value after the aggregation is finished

All Implemented Interfaces:

FunctionImplementation

Direct Known Subclasses:

ArbitraryAggregation, AverageAggregation, CollectSetAggregation, CountAggregation, GeometricMeanAggregation, MaximumAggregation, MinimumAggregation, StandardDeviationAggregation, SumAggregation, VarianceAggregation

public abstract class AggregationFunction<TPartial,TFinal>
extends java.lang.Object
implements FunctionImplementation

A special FunctionImplementation that compute a single result from a set of input values

Constructor Summary

Constructors

Constructor and Description
AggregationFunction()

Method Summary

Modifier and Type	Method and Description
abstract TPartial	iterate(RamAccountingContext ramAccountingContext, TPartial state, Input... args) the "aggregate" function.
abstract TPartial	newState(RamAccountingContext ramAccountingContext, org.elasticsearch.Version indexVersionCreated, org.elasticsearch.common.util.BigArrays bigArrays) Called once per "aggregation cycle" to create an initial partial-state-value.
abstract DataType	partialType()
abstract TPartial	reduce(RamAccountingContext ramAccountingContext, TPartial state1, TPartial state2) This function merges two aggregation states together and returns that merged state.
abstract TFinal	terminatePartial(RamAccountingContext ramAccountingContext, TPartial state) Called to transform partial states into their final form.

Methods inherited from class java.lang.Object

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

Methods inherited from interface io.crate.metadata.FunctionImplementation

info, normalizeSymbol

Constructor Detail

AggregationFunction

public AggregationFunction()

Method Detail

newState

@Nullable
public abstract TPartial newState(RamAccountingContext ramAccountingContext,
                                            org.elasticsearch.Version indexVersionCreated,
                                            org.elasticsearch.common.util.BigArrays bigArrays)

Called once per "aggregation cycle" to create an initial partial-state-value.

Parameters:

ramAccountingContext - used to account the memory used for the state.

indexVersionCreated - the version the current index was created on, this is useful for BWC

bigArrays - the BigArrays singleton instance of the current node

Returns:

a new state instance or null

iterate

public abstract TPartial iterate(RamAccountingContext ramAccountingContext,
                                 TPartial state,
                                 Input... args)
                          throws org.elasticsearch.common.breaker.CircuitBreakingException

the "aggregate" function.

Parameters:

ramAccountingContext - used to account for additional memory usage if the state grows in size

state - the previous aggregation state

args - arguments / input values matching the types of FunctionInfo.argumentTypes. These are usually used to increment/modify the previous state

Returns:

The new/changed state. This might be either a new instance or the same but mutated instance. Users of the AggregationFunction should always use the return value, but must be aware that the input state might have changed too.

Throws:

org.elasticsearch.common.breaker.CircuitBreakingException

reduce

public abstract TPartial reduce(RamAccountingContext ramAccountingContext,
                                TPartial state1,
                                TPartial state2)

This function merges two aggregation states together and returns that merged state.

This is used in a distributed aggregation workflow where 2 partial aggregations are reduced into 1 partial aggregation

Returns:

the reduced state. This might be a new instance or a mutated state1 or state2.

terminatePartial

public abstract TFinal terminatePartial(RamAccountingContext ramAccountingContext,
                                        TPartial state)

Called to transform partial states into their final form. This might result in a loss of "meta data" that was necessary to compute the final value.

partialType

public abstract DataType partialType()