com.bigdata.rdf.sparql.ast.optimizers

Class ASTSparql11SubqueryOptimizer

java.lang.Object

com.bigdata.rdf.sparql.ast.optimizers.ASTSparql11SubqueryOptimizer

All Implemented Interfaces:

IASTOptimizer

public class ASTSparql11SubqueryOptimizer
extends Object
implements IASTOptimizer

Lift SubqueryRoots into named subqueries when appropriate. This includes the following cases:

• Lift out SPARQL 1.1 subqueries which use both LIMIT and ORDER BY. Due to the interaction of the LIMIT and ORDER BY clause, these subqueries MUST be run first since they can produce different results if they are run "as-bound".
• Lift out SPARQL 1.1 subqueries involving aggregates. This typically provides more efficient evaluation than repeated as-bound evaluation of the sub-select. It also prevents inappropriate sharing of the internal state of the IAggregate functions.
• Lift out SPARQL 1.1 subqueries if there are no incoming bound variables which are also projected by the subquery. Such subqueries must be lifted or we will simply be doing the same work over and over since no bindings will be projected into the subquery.
• Lift out SPARQL 1.1 subqueries if SubqueryRoot.isRunOnce() is true.

FIXME The code to lift out sub-selects if there are no join variables has been disabled since we are not correctly computing the join variables at this point. Deciding the join variables requires that we either apply heuristics or the RTO to decide on a join ordering. Once the join order is known we can then recognize which variables will be definitely bound at the point in the join group where the subquery would be evaluated.

Version:

$Id: ASTSparql11SubqueryOptimizer.java 5193 2011-09-15 14:18:56Z thompsonbry $

Author:

Bryan Thompson

Constructor Summary

Constructors

Constructor and Description
ASTSparql11SubqueryOptimizer()

Method Summary

Methods

Modifier and Type	Method and Description
static boolean	needsLifting(SubqueryRoot subqueryRoot) Returns true iff the subquery needs to be lifted into a named subquery include.
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

ASTSparql11SubqueryOptimizer

public ASTSparql11SubqueryOptimizer()

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.

needsLifting

public static boolean needsLifting(SubqueryRoot subqueryRoot)

Returns true iff the subquery needs to be lifted into a named subquery include.

Parameters:

subqueryRoot -

Returns: