Class OrderByDistinctOptimiser

An optimizer that handles a special case for ORDER BY + DISTINCT combinations which can significantly improve performance by eliminating duplicates prior to sorting when the default SPARQL behaviour is to do a potentially costly sort over many duplicates and then eliminate distincts.
Inheritance
System.Object
OrderByDistinctOptimiser
Implements
Inherited Members
System.Object.Equals(System.Object)
System.Object.Equals(System.Object, System.Object)
System.Object.GetHashCode()
System.Object.GetType()
System.Object.MemberwiseClone()
System.Object.ReferenceEquals(System.Object, System.Object)
System.Object.ToString()
Namespace: VDS.RDF.Query.Optimisation
Assembly: dotNetRDF.dll
Syntax
public class OrderByDistinctOptimiser : IAlgebraOptimiser
Remarks
Only applies to queries which meet the following criteria:.
  • Has an ORDER BY and a DISTNCT on the same level of the query
  • Selects a fixed list of variables i.e. not a SELECT DISTINCT *
  • All variables used in the ORDER BY expressions also occur in the project list

Methods

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IsApplicable(SparqlQuery)

Returns true if the query is a SELECT DISTINCT or SELECT REDUCED and has an ORDER BY.
Declaration
public bool IsApplicable(SparqlQuery q)
Parameters
Type Name Description
SparqlQuery q Query.
Returns
Type Description
System.Boolean
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IsApplicable(SparqlUpdateCommandSet)

Returns that this is not applicable to updates.
Declaration
public bool IsApplicable(SparqlUpdateCommandSet cmds)
Parameters
Type Name Description
SparqlUpdateCommandSet cmds Update commands.
Returns
Type Description
System.Boolean
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Optimise(ISparqlAlgebra)

Optimizes the given algebra.
Declaration
public ISparqlAlgebra Optimise(ISparqlAlgebra algebra)
Parameters
Type Name Description
ISparqlAlgebra algebra Algebra.
Returns
Type Description
ISparqlAlgebra Optimized algebra.

Implements

Extension Methods