io.druid.query.aggregation

Interface AggregatorFactory

All Known Implementing Classes:

ApproximateHistogramAggregatorFactory, ApproximateHistogramFoldingAggregatorFactory, CardinalityAggregatorFactory, CountAggregatorFactory, DoubleSumAggregatorFactory, FilteredAggregatorFactory, HistogramAggregatorFactory, HyperUniquesAggregatorFactory, JavaScriptAggregatorFactory, LongSumAggregatorFactory, MaxAggregatorFactory, MinAggregatorFactory, ToLowerCaseAggregatorFactory

public interface AggregatorFactory

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.

Method Summary

Methods

Modifier and Type	Method and Description
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().
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.
Aggregator	factorize(ColumnSelectorFactory metricFactory)
BufferAggregator	factorizeBuffered(ColumnSelectorFactory metricFactory)
Object	finalizeComputation(Object object) "Finalizes" the computation of an object.
Object	getAggregatorStartValue() Returns the starting value for a corresponding aggregator.
byte[]	getCacheKey()
AggregatorFactory	getCombiningFactory() Returns an AggregatorFactory that can be used to combine the output of aggregators from this factory.
Comparator	getComparator()
int	getMaxIntermediateSize() Returns the maximum size that this aggregator will require in bytes for intermediate storage of results.
String	getName()
List<AggregatorFactory>	getRequiredColumns() Gets a list of all columns that this AggregatorFactory will scan
String	getTypeName()
List<String>	requiredFields()

Method Detail

factorize

Aggregator factorize(ColumnSelectorFactory metricFactory)

factorizeBuffered

BufferAggregator factorizeBuffered(ColumnSelectorFactory metricFactory)

getComparator

Comparator getComparator()

combine

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

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.

getRequiredColumns

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

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

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

String getName()

requiredFields

List<String> requiredFields()

getCacheKey

byte[] getCacheKey()

getTypeName

String getTypeName()

getMaxIntermediateSize

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.

getAggregatorStartValue

Object getAggregatorStartValue()

Returns the starting value for a corresponding aggregator. For example, 0 for sums, - Infinity for max, an empty mogrifier

Returns:

the starting value for a corresponding aggregator.