Package org.apache.druid.segment.virtual

Class SingleStringInputDeferredEvaluationExpressionDimensionVectorSelector

java.lang.Object

org.apache.druid.segment.virtual.SingleStringInputDeferredEvaluationExpressionDimensionVectorSelector

All Implemented Interfaces:

DimensionDictionarySelector, SingleValueDimensionVectorSelector, VectorSizeInspector

public class SingleStringInputDeferredEvaluationExpressionDimensionVectorSelector
extends Object
implements SingleValueDimensionVectorSelector

A SingleValueDimensionVectorSelector decorator that directly exposes the underlying dictionary ids in getRowVector(), saving expression computation until lookupName(int) is called. This allows for performing operations like grouping on the native dictionary ids, and deferring expression evaluation until after, which can dramatically reduce the total number of evaluations.

See Also:

for details on how expression vector selectors are constructed., for the non-vectorized version of this selector.

Field Summary

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

CARDINALITY_UNKNOWN

Constructor Summary

Constructors

Constructor	Description
SingleStringInputDeferredEvaluationExpressionDimensionVectorSelector(SingleValueDimensionVectorSelector selector, Expr expression)

Method Summary

Modifier and Type	Method	Description
int	getCurrentVectorSize()	Returns the current vector size for this cursor.
int	getMaxVectorSize()	Returns the maximum vector size for this cursor.
int[]	getRowVector()	Get the current vector.
int	getValueCardinality()	Value cardinality is the cardinality of the different occurring values.
IdLookup	idLookup()	Returns IdLookup if available for this DimensionSelector, or null.
String	lookupName(int id)	Returns the value for a particular dictionary id as a Java String.
boolean	nameLookupPossibleInAdvance()	Returns true if it is possible to DimensionDictionarySelector.lookupName(int) by ids from 0 to DimensionDictionarySelector.getValueCardinality() before the rows with those ids are returned.

Methods inherited from class java.lang.Object

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

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

lookupNameUtf8, supportsLookupNameUtf8

Constructor Detail

SingleStringInputDeferredEvaluationExpressionDimensionVectorSelector

public SingleStringInputDeferredEvaluationExpressionDimensionVectorSelector(SingleValueDimensionVectorSelector selector,
                                                                            Expr expression)

Method Detail

getValueCardinality

public int getValueCardinality()

Description copied from interface: DimensionDictionarySelector

Value cardinality is the cardinality of the different occurring values. If there were 4 rows: A,B A B A Value cardinality would be 2. Cardinality may be unknown (e.g. the selector used by IncrementalIndex while reading input rows), in which case this method will return -1. If cardinality is unknown, you should assume this dimension selector has no dictionary, and avoid storing ids, calling "lookupId", or calling "lookupName" outside of the context of operating on a single row. If cardinality is known then it is assumed that underlying dictionary is lexicographically sorted by the encoded value. For example if there are values "A" , "B" , "C" in a column with cardinality 3 then it is assumed that id("A") < id("B") < id("C")

Specified by:

getValueCardinality in interface DimensionDictionarySelector

Returns:

the value cardinality, or DimensionDictionarySelector.CARDINALITY_UNKNOWN if unknown.

lookupName

@Nullable
public String lookupName(int id)

Description copied from interface: DimensionDictionarySelector

Returns the value for a particular dictionary id as a Java String. For example, if a column has four rows: A,B A A,B B getRow() would return getRow(0) => [0 1] getRow(1) => [0] getRow(2) => [0 1] getRow(3) => [1] and then lookupName would return: lookupName(0) => A lookupName(1) => B Performance note: if you want a java.lang.String, always use this method. It will be at least as fast as calling DimensionDictionarySelector.lookupNameUtf8(int) and decoding the bytes. However, if you want UTF-8 bytes, then check if DimensionDictionarySelector.supportsLookupNameUtf8() returns true, and if it does, use DimensionDictionarySelector.lookupNameUtf8(int) instead.

Specified by:

lookupName in interface DimensionDictionarySelector

Parameters:

id - id to lookup the dictionary value for

Returns:

dictionary value for the given id, or null if the value is itself null

nameLookupPossibleInAdvance

public boolean nameLookupPossibleInAdvance()

Description copied from interface: DimensionDictionarySelector

Returns true if it is possible to DimensionDictionarySelector.lookupName(int) by ids from 0 to DimensionDictionarySelector.getValueCardinality() before the rows with those ids are returned.

Returns false if DimensionDictionarySelector.lookupName(int) could be called with ids, returned from the most recent row (or row vector) returned by this DimensionSelector, but not earlier. If DimensionDictionarySelector.getValueCardinality() of this selector additionally returns DimensionDictionarySelector.CARDINALITY_UNKNOWN, lookupName() couldn't be called with ids, returned by not the most recent row (or row vector), i. e. names for ids couldn't be looked up "later". If DimensionDictionarySelector.getValueCardinality() returns a non-negative number, lookupName() could be called with any ids, returned from rows (or row vectors) returned since the creation of this DimensionSelector.

If DimensionDictionarySelector.lookupName(int) is called with an ineligible id, result is undefined: exception could be thrown, or null returned, or some other random value.

Specified by:

nameLookupPossibleInAdvance in interface DimensionDictionarySelector

idLookup

@Nullable
public IdLookup idLookup()

Description copied from interface: DimensionDictionarySelector

Returns IdLookup if available for this DimensionSelector, or null.

Specified by:

idLookup in interface DimensionDictionarySelector

getRowVector

public int[] getRowVector()

Description copied from interface: SingleValueDimensionVectorSelector

Get the current vector. The array will be reused, so it is not a good idea to retain a reference to it.

Specified by:

getRowVector in interface SingleValueDimensionVectorSelector

getMaxVectorSize

public int getMaxVectorSize()

Description copied from interface: VectorSizeInspector

Returns the maximum vector size for this cursor. It will not change for the lifetime of this cursor, and is generally used to allocate scratch arrays for later processing. Will always be greater than zero.

Specified by:

getMaxVectorSize in interface VectorSizeInspector

getCurrentVectorSize

public int getCurrentVectorSize()

Description copied from interface: VectorSizeInspector

Returns the current vector size for this cursor. Will never be larger than the max size returned by VectorSizeInspector.getMaxVectorSize().

Specified by:

getCurrentVectorSize in interface VectorSizeInspector