Package org.eclipse.rdf4j.sail.extensiblestore.evaluationstatistics

Class ExtensibleDynamicEvaluationStatistics

java.lang.Object

org.eclipse.rdf4j.query.algebra.evaluation.impl.EvaluationStatistics

org.eclipse.rdf4j.sail.extensiblestore.evaluationstatistics.ExtensibleEvaluationStatistics

org.eclipse.rdf4j.sail.extensiblestore.evaluationstatistics.ExtensibleDynamicEvaluationStatistics

All Implemented Interfaces:

DynamicStatistics

@Experimental
public class ExtensibleDynamicEvaluationStatistics
extends ExtensibleEvaluationStatistics
implements DynamicStatistics

ExtensibleDynamicEvaluationStatistics aims to keep an internal estimate of the cardinality of various statement patterns.

It support getting the overall size, any single dimension cardinality (eg. ?a rdf:type ?b) and also two multidimensional patterns (:Peter rdf:type ?b; and ?a rdf:type foaf:Person).

Since evaluation statistics are best-effort, we use HLL as sets to keep the number of statements for each pattern we support. HLL is a very memory efficient set implementation. Furthermore we hash each pattern into a fixed bucket size, 1024 for single dimension and 64 per dimension for multidimensional patterns.

This means that adding ':peter rdf:type foaf:Person' and ':lisa rdf:type foaf:Person' could potentially return getCardinality(:peter, ?b, ?c) = 2 if both :peter and :lisa hash to the same of the 1024 buckets in subjectIndex.

HLL does not support "remove" operations, so there are two sets of every index. One for all added statements and one for all removed statements. If the user adds, removes and re-adds the same statement then the cardinality for that statement will be incorrect. We call this effect "staleness". To prevent staleness from affecting the returned cardinalities this class needs to be monitored by calling the staleness(...) method. This will automatically be done every 60 seconds by the ExtensibleSailStore.

Nested Class Summary

Nested classes/interfaces inherited from class org.eclipse.rdf4j.query.algebra.evaluation.impl.EvaluationStatistics

EvaluationStatistics.CardinalityCalculator

Constructor Summary

Constructors

Constructor	Description
ExtensibleDynamicEvaluationStatistics(ExtensibleSailStore extensibleSailStore)

Method Summary

Modifier and Type	Method	Description
void	add(ExtensibleStatement statement)
protected EvaluationStatistics.CardinalityCalculator	createCardinalityCalculator()
void	remove(ExtensibleStatement statement)
void	removeByQuery(Resource subj, IRI pred, Value obj, boolean inferred, Resource... contexts)
double	staleness(long expectedSize)
void	waitForQueue()

Methods inherited from class org.eclipse.rdf4j.query.algebra.evaluation.impl.EvaluationStatistics

getCardinality

Methods inherited from class java.lang.Object

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

Constructor Details

ExtensibleDynamicEvaluationStatistics

public ExtensibleDynamicEvaluationStatistics(ExtensibleSailStore extensibleSailStore)

Method Details

createCardinalityCalculator

protected EvaluationStatistics.CardinalityCalculator createCardinalityCalculator()

Specified by:

createCardinalityCalculator in class ExtensibleEvaluationStatistics

staleness

public double staleness(long expectedSize)

Specified by:

staleness in interface DynamicStatistics

Returns:

1 if stale, 0 if not stale, 0.5 if 50% stale. Seen as, given a random statement (that has either been added, or removed), what is the probability that the statistics will return an incorrect result?

add

public void add(ExtensibleStatement statement)

Specified by:

add in interface DynamicStatistics

remove

public void remove(ExtensibleStatement statement)

Specified by:

remove in interface DynamicStatistics

removeByQuery

public void removeByQuery(Resource subj,
 IRI pred,
 Value obj,
 boolean inferred,
 Resource... contexts)

Specified by:

removeByQuery in interface DynamicStatistics

waitForQueue

public void waitForQueue()
                  throws InterruptedException

Throws:

InterruptedException