org.modeshape.jcr.query.optimize
Class RewriteIdentityJoins

java.lang.Object
  org.modeshape.jcr.query.optimize.RewriteIdentityJoins

All Implemented Interfaces:

OptimizerRule

@Immutable
public class RewriteIdentityJoins
extends Object
implements OptimizerRule

An optimizer rule that rewrites JOIN nodes that have equi-join criteria where the columns involved in the equi-join are all identity columns (that is, they form a key for the table). This rewrite only happens when the left and right children of the JOIN node are both SOURCE nodes.

The basic idea is that in these identity equi-join cases, the following structure:

          ...
           |
         JOIN
        /     \
       /       \
   SOURCE     SOURCE
 

is transformed into a simple SOURCE node:

        ...
         |
       SOURCE
 

Note that this rewriting removes a selector, and thus the nodes above the JOIN node that made use of the removed selector are also modified to reference the remaining selector.

Field Summary

static RewriteIdentityJoins

INSTANCE

Constructor Summary

RewriteIdentityJoins()

Method Summary

PlanNode	execute(QueryContext context, PlanNode plan, LinkedList<OptimizerRule> ruleStack) Optimize the supplied plan using the supplied context, hints, and yet-to-be-run rules.
protected void	rewriteJoinNode(QueryContext context, PlanNode joinNode, Map<SelectorName,SelectorName> rewrittenSelectors)
String	toString()

Methods inherited from class java.lang.Object

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

Field Detail

INSTANCE

public static final RewriteIdentityJoins INSTANCE

Constructor Detail

RewriteIdentityJoins

public RewriteIdentityJoins()

Method Detail

execute

public PlanNode execute(QueryContext context,
                        PlanNode plan,
                        LinkedList<OptimizerRule> ruleStack)

Description copied from interface: OptimizerRule

Optimize the supplied plan using the supplied context, hints, and yet-to-be-run rules.

Specified by:

execute in interface OptimizerRule

Parameters:

context - the context in which the query is being optimized; never null

plan - the plan to be optimized; never null

ruleStack - the stack of rules that will be run after this rule; never null

Returns:

the optimized plan; never null

rewriteJoinNode

protected void rewriteJoinNode(QueryContext context,
                               PlanNode joinNode,
                               Map<SelectorName,SelectorName> rewrittenSelectors)

toString

public String toString()

Overrides:

toString in class Object