org.jboss.dna.graph.query.optimize
Class ChooseJoinAlgorithm

java.lang.Object
  org.jboss.dna.graph.query.optimize.ChooseJoinAlgorithm

All Implemented Interfaces:

OptimizerRule

@Immutable
public class ChooseJoinAlgorithm
extends Object
implements OptimizerRule

An optimizer rule that choose the appropriate join algorithm and sets up any prerequisites, based upon the JoinCondition.

There are two static instances that can be used (or the equivalent can be instantiated or subclassed using the constructor): one that only uses nested-loop, and another that will attempt to use merge where possible. Both instances ignore any existing PlanNode.Property.JOIN_ALGORITHM property value set on the JOIN node.

For example, the USE_ONLY_NESTED_JOIN_ALGORITHM instance will convert this simple tree:

          ...
           |
         JOIN
        /     \
      ...     ...
 

into this:

          ...
           |
         JOIN (JOIN_ALGORITHM=NESTED_LOOP)
        /     \
      ...     ...
 

On the other hand, the USE_BEST_JOIN_ALGORITHM instance will do a couple of different things, depending upon the input plan.

1. If the condition is a DescendantNodeJoinCondition, then the join algorithm will always be JoinAlgorithm.NESTED_LOOP.
2. Otherwise, the rule will use the JoinAlgorithm.MERGE algorithm and will change this structure:

             ...
              |
            JOIN
           /     \
         ...     ...
    

   into this:

             ...
              |
            JOIN (JOIN_ALGORITHM=MERGE)
           /     \
          /       \
    DUP_REMOVE  DUP_REMOVE
        |           |
       SORT       SORT
        |           |
       ...         ...
    

Field Summary

static ChooseJoinAlgorithm	USE_BEST_JOIN_ALGORITHM
static ChooseJoinAlgorithm	USE_ONLY_NESTED_JOIN_ALGORITHM

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.
String	toString()

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

USE_ONLY_NESTED_JOIN_ALGORITHM

public static final ChooseJoinAlgorithm USE_ONLY_NESTED_JOIN_ALGORITHM

USE_BEST_JOIN_ALGORITHM

public static final ChooseJoinAlgorithm USE_BEST_JOIN_ALGORITHM

Method Detail

execute

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

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

See Also:

OptimizerRule.execute(org.jboss.dna.graph.query.QueryContext, org.jboss.dna.graph.query.plan.PlanNode, java.util.LinkedList)

toString

public String toString()

Overrides:

toString in class Object

See Also:

Object.toString()