io.druid.query.aggregation

Class AggregatorFactory

java.lang.Object

io.druid.query.aggregation.AggregatorFactory

All Implemented Interfaces:

Cacheable

Direct Known Subclasses:

ApproximateHistogramAggregatorFactory, CardinalityAggregatorFactory, CountAggregatorFactory, DistinctCountAggregatorFactory, DoubleFirstAggregatorFactory, DoubleLastAggregatorFactory, DoubleMaxAggregatorFactory, DoubleMinAggregatorFactory, DoubleSumAggregatorFactory, FilteredAggregatorFactory, HistogramAggregatorFactory, HyperUniquesAggregatorFactory, JavaScriptAggregatorFactory, LongFirstAggregatorFactory, LongLastAggregatorFactory, LongMaxAggregatorFactory, LongMinAggregatorFactory, LongSumAggregatorFactory, SketchAggregatorFactory, TimestampAggregatorFactory, VarianceAggregatorFactory

public abstract class AggregatorFactory
extends Object
implements Cacheable

Processing related interface An AggregatorFactory is an object that knows how to generate an Aggregator using a ColumnSelectorFactory. This is useful as an abstraction to allow Aggregator classes to be written in terms of MetricSelector objects without making any assumptions about how they are pulling values out of the base data. That is, the data is provided to the Aggregator through the MetricSelector object, so whatever creates that object gets to choose how the data is actually stored and accessed.

Constructor Summary

Constructors

Constructor and Description
AggregatorFactory()

Method Summary

Modifier and Type	Method and Description
abstract Object	combine(Object lhs, Object rhs) A method that knows how to combine the outputs of the getIntermediate() method from the Aggregators produced via factorize().
abstract Object	deserialize(Object object) A method that knows how to "deserialize" the object from whatever form it might have been put into in order to transfer via JSON.
abstract Aggregator	factorize(ColumnSelectorFactory metricFactory)
abstract BufferAggregator	factorizeBuffered(ColumnSelectorFactory metricFactory)
abstract Object	finalizeComputation(Object object) "Finalizes" the computation of an object.
abstract AggregatorFactory	getCombiningFactory() Returns an AggregatorFactory that can be used to combine the output of aggregators from this factory.
abstract Comparator	getComparator()
abstract int	getMaxIntermediateSize() Returns the maximum size that this aggregator will require in bytes for intermediate storage of results.
AggregatorFactory	getMergingFactory(AggregatorFactory other) Returns an AggregatorFactory that can be used to merge the output of aggregators from this factory and other factory.
abstract String	getName()
abstract List<AggregatorFactory>	getRequiredColumns() Gets a list of all columns that this AggregatorFactory will scan
abstract String	getTypeName()
static AggregatorFactory[]	mergeAggregators(List<AggregatorFactory[]> aggregatorsList) Merges the list of AggregatorFactory[] (presumable from metadata of some segments being merged) and returns merged AggregatorFactory[] (for the metadata for merged segment).
abstract List<String>	requiredFields()

Methods inherited from class java.lang.Object

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

Methods inherited from interface io.druid.java.util.common.Cacheable

getCacheKey

Constructor Detail

AggregatorFactory

public AggregatorFactory()

Method Detail

factorize

public abstract Aggregator factorize(ColumnSelectorFactory metricFactory)

factorizeBuffered

public abstract BufferAggregator factorizeBuffered(ColumnSelectorFactory metricFactory)

getComparator

public abstract Comparator getComparator()

combine

public abstract Object combine(Object lhs,
                               Object rhs)

A method that knows how to combine the outputs of the getIntermediate() method from the Aggregators produced via factorize(). Note, even though this is called combine, this method's contract *does* allow for mutation of the input objects. Thus, any use of lhs or rhs after calling this method is highly discouraged.

Parameters:

lhs - The left hand side of the combine

rhs - The right hand side of the combine

Returns:

an object representing the combination of lhs and rhs, this can be a new object or a mutation of the inputs

getCombiningFactory

public abstract AggregatorFactory getCombiningFactory()

Returns an AggregatorFactory that can be used to combine the output of aggregators from this factory. This generally amounts to simply creating a new factory that is the same as the current except with its input column renamed to the same as the output column.

Returns:

a new Factory that can be used for operations on top of data output from the current factory.

getMergingFactory

public AggregatorFactory getMergingFactory(AggregatorFactory other)
                                    throws AggregatorFactoryNotMergeableException

Returns an AggregatorFactory that can be used to merge the output of aggregators from this factory and other factory. This method is relevant only for AggregatorFactory which can be used at ingestion time.

Returns:

a new Factory that can be used for merging the output of aggregators from this factory and other.

Throws:

AggregatorFactoryNotMergeableException

getRequiredColumns

public abstract List<AggregatorFactory> getRequiredColumns()

Gets a list of all columns that this AggregatorFactory will scan

Returns:

AggregatorFactories for the columns to scan of the parent AggregatorFactory

deserialize

public abstract Object deserialize(Object object)

A method that knows how to "deserialize" the object from whatever form it might have been put into in order to transfer via JSON.

Parameters:

object - the object to deserialize

Returns:

the deserialized object

finalizeComputation

public abstract Object finalizeComputation(Object object)

"Finalizes" the computation of an object. Primarily useful for complex types that have a different mergeable intermediate format than their final resultant output.

Parameters:

object - the object to be finalized

Returns:

the finalized value that should be returned for the initial query

getName

public abstract String getName()

requiredFields

public abstract List<String> requiredFields()

getTypeName

public abstract String getTypeName()

getMaxIntermediateSize

public abstract int getMaxIntermediateSize()

Returns the maximum size that this aggregator will require in bytes for intermediate storage of results.

Returns:

the maximum number of bytes that an aggregator of this type will require for intermediate result storage.

mergeAggregators

public static AggregatorFactory[] mergeAggregators(List<AggregatorFactory[]> aggregatorsList)

Merges the list of AggregatorFactory[] (presumable from metadata of some segments being merged) and returns merged AggregatorFactory[] (for the metadata for merged segment). Null is returned if it is not possible to do the merging for any of the following reason. - one of the element in input list is null i.e. aggregators for one the segments being merged is unknown - AggregatorFactory of same name can not be merged if they are not compatible

Parameters:

aggregatorsList -

Returns:

merged AggregatorFactory[] or Null if merging is not possible.