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
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 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

Properties

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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
System.Boolean
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
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
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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
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
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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.
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

Implements

Extension Methods