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
object
OrderByDistinctOptimiser
Implements
Inherited Members
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
bool

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
bool
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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
bool
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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