Package org.apache.druid.query.aggregation

Class SingleValueAggregatorFactory

java.lang.Object

org.apache.druid.query.aggregation.AggregatorFactory

org.apache.druid.query.aggregation.SingleValueAggregatorFactory

All Implemented Interfaces:

Cacheable

public class SingleValueAggregatorFactory
extends AggregatorFactory

This AggregatorFactory is meant to wrap the subquery used as an expression into a single value and is expected to throw an exception when the subquery results in more than one row

This consumes columnType as well along with name and fieldName to pass it on to underlying SingleValueBufferAggregator to work with different ColumnTypes

Field Summary

Fields

Modifier and Type	Field	Description
static final int	DEFAULT_MAX_VALUE_SIZE

Constructor Summary

Constructors

Constructor	Description
SingleValueAggregatorFactory(String name, String fieldName, ColumnType columnType)

Method Summary

Modifier and Type	Method	Description
Object	combine(Object lhs, Object rhs)	Combine method would never be invoked as the broker sends the subquery to multiple segments and gather the results to a single value on which the single value aggregator is applied.
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.
boolean	equals(Object o)
Aggregator	factorize(ColumnSelectorFactory metricFactory)
BufferAggregator	factorizeBuffered(ColumnSelectorFactory metricFactory)
Object	finalizeComputation(Object object)	"Finalizes" the computation of an object.
byte[]	getCacheKey()	Get a byte array used as a cache key.
AggregatorFactory	getCombiningFactory()	Returns an AggregatorFactory that can be used to combine the output of aggregators from this factory.
Comparator	getComparator()
String	getFieldName()
ColumnType	getIntermediateType()	Get the "intermediate" ColumnType for this aggregator.
int	getMaxIntermediateSize()	Returns the maximum size that this aggregator will require in bytes for intermediate storage of results.
String	getName()
ColumnType	getResultType()	Get the ColumnType for the final form of this aggregator, i.e.
int	hashCode()
List<String>	requiredFields()	Get a list of fields that aggregators built by this factory will need to read.
String	toString()

Methods inherited from class org.apache.druid.query.aggregation.AggregatorFactory

canVectorize, factorizeVector, factorizeWithSize, getComplexTypeName, getFinalizedType, getMaxIntermediateSizeWithNulls, getMergingFactory, getRequiredColumns, getType, guessAggregatorHeapFootprint, makeAggregateCombiner, makeNullableAggregateCombiner, mergeAggregators, optimizeForSegment, substituteCombiningFactory, withName

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Details

DEFAULT_MAX_VALUE_SIZE

public static final int DEFAULT_MAX_VALUE_SIZE

See Also:

• Constant Field Values

Constructor Details

SingleValueAggregatorFactory

public SingleValueAggregatorFactory(String name,
 String fieldName,
 ColumnType columnType)

Method Details

factorize

public Aggregator factorize(ColumnSelectorFactory metricFactory)

Specified by:

factorize in class AggregatorFactory

factorizeBuffered

public BufferAggregator factorizeBuffered(ColumnSelectorFactory metricFactory)

Specified by:

factorizeBuffered in class AggregatorFactory

getComparator

public Comparator getComparator()

Specified by:

getComparator in class AggregatorFactory

combine

@Nullable
public Object combine(@Nullable
 Object lhs,
 @Nullable
 Object rhs)

Combine method would never be invoked as the broker sends the subquery to multiple segments and gather the results to a single value on which the single value aggregator is applied. Though getCombiningFactory would be invoked for understanding the fieldname.

Specified by:

combine in class AggregatorFactory

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 AggregatorFactory getCombiningFactory()

Description copied from class: AggregatorFactory

Returns an AggregatorFactory that can be used to combine the output of aggregators from this factory. It is used when we know we have some values that were produced with this aggregator factory, and want to do some additional combining of them. This happens, for example, when merging query results from two different segments, or two different servers. For simple aggregators, the combining factory may be computed by 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. For example, this aggregator: {"type": "longSum", "fieldName": "foo", "name": "bar"} Would become: {"type": "longSum", "fieldName": "bar", "name": "bar"} Sometimes, the type or other parameters of the combining aggregator will be different from the original aggregator. For example, the CountAggregatorFactory getCombiningFactory method will return a LongSumAggregatorFactory, because counts are combined by summing. No matter what, `foo.getCombiningFactory()` and `foo.getCombiningFactory().getCombiningFactory()` should return the same result.

Specified by:

getCombiningFactory in class AggregatorFactory

Returns:

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

deserialize

public Object deserialize(Object object)

Description copied from class: AggregatorFactory

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

Specified by:

deserialize in class AggregatorFactory

Parameters:

object - the object to deserialize

Returns:

the deserialized object

finalizeComputation

@Nullable
public Object finalizeComputation(@Nullable
 Object object)

Description copied from class: AggregatorFactory

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

Specified by:

finalizeComputation in class AggregatorFactory

Parameters:

object - the object to be finalized

Returns:

the finalized value that should be returned for the initial query

getIntermediateType

public ColumnType getIntermediateType()

Description copied from class: AggregatorFactory

Get the "intermediate" ColumnType for this aggregator. This is the same as the type returned by AggregatorFactory.deserialize(java.lang.Object) and the type accepted by AggregatorFactory.combine(java.lang.Object, java.lang.Object). However, it is *not* necessarily the same type returned by AggregatorFactory.finalizeComputation(java.lang.Object). Refer to the ColumnType javadocs for details on the implications of choosing a type.

Overrides:

getIntermediateType in class AggregatorFactory

getResultType

public ColumnType getResultType()

Description copied from class: AggregatorFactory

Get the ColumnType for the final form of this aggregator, i.e. the type of the value returned by AggregatorFactory.finalizeComputation(java.lang.Object). This may be the same as or different than the types expected in AggregatorFactory.deserialize(java.lang.Object) and AggregatorFactory.combine(java.lang.Object, java.lang.Object). Refer to the ColumnType javadocs for details on the implications of choosing a type.

Overrides:

getResultType in class AggregatorFactory

getName

public String getName()

Specified by:

getName in class AggregatorFactory

Returns:

output name of the aggregator column.

getFieldName

public String getFieldName()

requiredFields

public List<String> requiredFields()

Description copied from class: AggregatorFactory

Get a list of fields that aggregators built by this factory will need to read.

Specified by:

requiredFields in class AggregatorFactory

getMaxIntermediateSize

public int getMaxIntermediateSize()

Description copied from class: AggregatorFactory

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

Specified by:

getMaxIntermediateSize in class AggregatorFactory

Returns:

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

getCacheKey

public byte[] getCacheKey()

Description copied from interface: Cacheable

Get a byte array used as a cache key.

Returns:

bytes to be used as cache key - or null if this object should not be cached.

equals

public boolean equals(Object o)

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object

toString

public String toString()

Overrides:

toString in class Object