Package org.apache.druid.query.aggregation

Interface AggregateCombiner<T>

All Superinterfaces:

BaseDoubleColumnValueSelector, BaseFloatColumnValueSelector, BaseLongColumnValueSelector, BaseNullableColumnValueSelector, BaseObjectColumnValueSelector<T>, ColumnValueSelector<T>, HotLoopCallee

All Known Implementing Classes:

DoubleAggregateCombiner, GenericFirstAggregateCombiner, GenericLastAggregateCombiner, HyperLogLogCollectorAggregateCombiner, LongAggregateCombiner, LongSumAggregateCombiner, NullableNumericAggregateCombiner, ObjectAggregateCombiner

public interface AggregateCombiner<T>
extends ColumnValueSelector<T>

AggregateCombiner is used to fold rollup aggregation results from serveral "rows" of different indexes during index merging (see IndexMerger). The state of the implementations of this interface is an aggregation value (either a primitive or an object), that could be queried via ColumnValueSelector's methods. Before reset(org.apache.druid.segment.ColumnValueSelector) is ever called on an AggregateCombiner, it's state is undefined and ColumnValueSelector's methods could return something random, or null, or throw an exception. This interface would probably better be called "AggregateFolder", but somebody may confuse it with "folder" as "directory" synonym.

See Also:

AggregatorFactory.makeAggregateCombiner(), LongAggregateCombiner, DoubleAggregateCombiner, ObjectAggregateCombiner

Field Summary

Fields inherited from interface org.apache.druid.segment.ColumnValueSelector

EMPTY_ARRAY

Method Summary

Modifier and Type	Method	Description
void	fold(ColumnValueSelector selector)	Folds this AggregateCombiner's state value with the value of the given selector and saves it in this AggregateCombiner's state, e.
default void	inspectRuntimeShape(RuntimeShapeInspector inspector)	Implementations of this method should call inspector.visit() with all fields of this class, which meet two conditions: 1.
default boolean	isNull()	Returns true if the primitive long, double, or float value returned by this selector should be treated as null.
void	reset(ColumnValueSelector selector)	Resets this AggregateCombiner's state value to the value of the given selector, e.

Methods inherited from interface org.apache.druid.segment.BaseDoubleColumnValueSelector

getDouble

Methods inherited from interface org.apache.druid.segment.BaseFloatColumnValueSelector

getFloat

Methods inherited from interface org.apache.druid.segment.BaseLongColumnValueSelector

getLong

Methods inherited from interface org.apache.druid.segment.BaseObjectColumnValueSelector

classOfObject, getObject

Method Detail

reset

void reset(ColumnValueSelector selector)

Resets this AggregateCombiner's state value to the value of the given selector, e. g. after calling this method combiner.get*() should return the same value as selector.get*(). If the selector is an ObjectColumnSelector, the object returned from BaseObjectColumnValueSelector.getObject() must not be modified, and must not become a subject for modification during subsequent fold(org.apache.druid.segment.ColumnValueSelector) calls.

fold

void fold(ColumnValueSelector selector)

Folds this AggregateCombiner's state value with the value of the given selector and saves it in this AggregateCombiner's state, e. g. after calling combiner.fold(selector), combiner.get*() should return the value that would be the result of aggregatorFactory.combine(combiner.get*(), selector.get*()) call. Unlike AggregatorFactory.combine(java.lang.Object, java.lang.Object), if the selector is an ObjectColumnSelector, the object returned from BaseObjectColumnValueSelector.getObject() must not be modified, and must not become a subject for modification during subsequent fold() calls. Since the state of AggregateCombiner is undefined before reset(org.apache.druid.segment.ColumnValueSelector) is ever called on it, the effects of calling fold() are also undefined in this case.

See Also:

AggregatorFactory.combine(java.lang.Object, java.lang.Object)

isNull

default boolean isNull()

Description copied from interface: BaseNullableColumnValueSelector

Returns true if the primitive long, double, or float value returned by this selector should be treated as null. Users of BaseLongColumnValueSelector.getLong(), BaseDoubleColumnValueSelector.getDouble() and BaseFloatColumnValueSelector.getFloat() must check this method first, or else they may improperly use placeholder values returned by the primitive get methods. Users of BaseObjectColumnValueSelector.getObject() should not call this method. Instead, call "getObject" and check if it is null.

Specified by:

isNull in interface BaseNullableColumnValueSelector

inspectRuntimeShape

default void inspectRuntimeShape(RuntimeShapeInspector inspector)

Description copied from interface: HotLoopCallee

Implementations of this method should call inspector.visit() with all fields of this class, which meet two conditions: 1. They are used in methods of this class, annotated with CalledFromHotLoop 2. They are either: a. Nullable objects b. Instances of HotLoopCallee c. Objects, which don't always have a specific class in runtime. For example, a field of type Set could be HashSet or TreeSet in runtime, depending on how this instance (the instance on which inspectRuntimeShape() is called) is configured. d. ByteBuffer or similar objects, where byte order matters e. boolean flags, affecting branch taking f. Arrays of objects, meeting any of conditions a-e.

Specified by:

inspectRuntimeShape in interface HotLoopCallee