io.druid.query.aggregation

Interface AggregateCombiner<T>

All Superinterfaces:

ColumnValueSelector<T>

All Known Implementing Classes:

DoubleAggregateCombiner, HyperLogLogCollectorAggregateCombiner, LongAggregateCombiner, LongSumAggregateCombiner, 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(io.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

Method Summary

Modifier and Type	Method and 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.
void	reset(ColumnValueSelector selector) Resets this AggregateCombiner's state value to the value of the given selector, e.

Methods inherited from interface io.druid.segment.ColumnValueSelector

classOfObject, getDouble, getFloat, getLong, 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 ColumnValueSelector.getObject() must not be modified, and must not become a subject for modification during subsequent fold(io.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 ColumnValueSelector.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(io.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)