Class ParallelEvaluationOptimiser

An Algebra Optimiser which looks for unions and joins that can be evaluated in parallel to improve query evaluation speed in some cases.

Inheritance

object

ParallelEvaluationOptimiser

Implements

IAlgebraOptimiser

Inherited Members

object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.MemberwiseClone()

object.ReferenceEquals(object, object)

object.ToString()

Namespace: VDS.RDF.Query.Optimisation

Assembly: dotNetRdf.dll

Syntax

public class ParallelEvaluationOptimiser : IAlgebraOptimiser

Remarks

Using this feature allows you to use experimental parallel SPARQL evaluation optimisations which may improve query evaluation speed for some queries. A query must either use UNION or have joins which are disjoint in order for any parallel evaluation to take place.

Users should be aware that using this optimiser may actually increase evaluation speed in some cases e.g. where either side of a disjoint join will return empty especially when it is the left hand side that will do so.

Also note that while use of this optimiser should not cause queries to return incorrect results as it does not change the semantics of the evaluation as it only parallelises independent operators we cannot guarantee that all parallelised queries will return identical results to their non-parallelised counterparts. If you find a query that you believe is giving incorrect results when used with this optimiser please test without the optimiser enabled to check that the apparent incorrect result is not an artifact of this optimisation.

Properties

UnsafeOptimisation

Determines whether an Optimiser will perform algebra optimizations that are potentially unsafe at execution time.

Declaration

public bool UnsafeOptimisation { get; set; }

Property Value

Type	Description
bool

Methods

IsApplicable(SparqlQuery)

Returns that the optimser is applicable to all queries.

Declaration

public bool IsApplicable(SparqlQuery q)

Parameters

Type	Name	Description
SparqlQuery	q	Query.

Returns

Type	Description
bool

IsApplicable(SparqlUpdateCommandSet)

Returns that the optimiser is not applicable to updates.

Declaration

public bool IsApplicable(SparqlUpdateCommandSet cmds)

Parameters

Type	Name	Description
SparqlUpdateCommandSet	cmds	Updates.

Returns

Type	Description
bool

Optimise(ISparqlAlgebra)

Optimises the algebra to use parallelised variants of Join and Union where possible.

Declaration

public ISparqlAlgebra Optimise(ISparqlAlgebra algebra)

Parameters

Type	Name	Description
ISparqlAlgebra	algebra	Algebra.

Returns

Type	Description
ISparqlAlgebra

Implements

IAlgebraOptimiser

Extension Methods

Extensions.ToSafeString(object)

Extensions.AsEnumerable<T>(T)