com.bigdata.rdf.sparql.ast.optimizers

Class ASTDistinctTermScanOptimizer

java.lang.Object

com.bigdata.rdf.sparql.ast.optimizers.ASTDistinctTermScanOptimizer

All Implemented Interfaces:

IASTOptimizer

public class ASTDistinctTermScanOptimizer
extends Object
implements IASTOptimizer

Optimizes SELECT (DISTINCT|REDUCED) ?property WHERE { ?x ?property ?y . } and similar patterns using an O(N) algorithm, where N is the number of distinct solutions.

The main advantage here is to turn an access path that is fully unbound into a distinct-term scan. If the access path would be evaluated as-bound with at least one variable bound, then the distinct term scan might not have any advantage over the pipeline join (and the semantics of DISTINCT would be violated with multiple as-bound evaluations of the distinct-term-scan without a hash index to impose the DISTINCT constraint). TODO We are doing something very similar for GRAPH ?g {}. It would be worth while to look at that code in the light of this optimizer.

Author:

Bryan Thompson

See Also:

DISTINCT PREDICATEs query is slow

Constructor Summary

Constructors

Constructor and Description
ASTDistinctTermScanOptimizer()

Method Summary

Methods

Modifier and Type	Method and Description
QueryNodeWithBindingSet	optimize(AST2BOpContext context, QueryNodeWithBindingSet input) Optimize the AST.

Methods inherited from class java.lang.Object

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

Constructor Detail

ASTDistinctTermScanOptimizer

public ASTDistinctTermScanOptimizer()

Method Detail

optimize

public QueryNodeWithBindingSet optimize(AST2BOpContext context,
                               QueryNodeWithBindingSet input)

Description copied from interface: IASTOptimizer

Optimize the AST.

Specified by:

optimize in interface IASTOptimizer

Parameters:

context - The evaluation context.

input - The input to the optimizer, consisting of a queryNode and input binding set.

Returns:

An instance of type QueryNodeWithBindingSet.