org.modeshape.jcr.query.optimize

Class PushSelectCriteria

java.lang.Object

org.modeshape.jcr.query.optimize.PushSelectCriteria

All Implemented Interfaces:

OptimizerRule

@Immutable
public class PushSelectCriteria
extends Object
implements OptimizerRule

An optimizer rule that attempts to push the criteria nodes in a canonical plan down as far as possible.

For example, here is a single-access plan before:

          ...
           |
        PROJECT      with the list of columns being SELECTed
           |
        SELECT1
           |         One or more SELECT plan nodes that each have
        SELECT2      a single non-join constraint that are then all AND-ed
           |         together
        SELECTn
           |
        ACCESS
           |
        SOURCE
 

And after:

          ...
           |
        ACCESS
           |
        PROJECT      with the list of columns being SELECTed
           |
        SELECT1
           |         One or more SELECT plan nodes that each have
        SELECT2      a single non-join constraint that are then all AND-ed
           |         together
        SELECTn
           |
        SOURCE
 

Here is another case, where multiple SELECT nodes above a simple JOIN and where each SELECT node applies to one or more of the SOURCE nodes (via the named selectors). Each SELECT node that applies to a single selector will get pushed toward that source, but will have the same order relative to other SELECT nodes also pushed toward that SOURCE. However, this rules does not push SELECT nodes that apply to multiple selectors.

Before:

          ...
           |
        PROJECT ('s1','s2')      with the list of columns being SELECTed (from 's1' and 's2' selectors)
           |
        SELECT1 ('s1')
           |                     One or more SELECT plan nodes that each have
        SELECT2 ('s2')           a single non-join constraint that are then all AND-ed
           |                     together, and that each have the selector(s) they apply to
        SELECT3 ('s1','s2')
           |
        SELECT4 ('s1')
           |
         JOIN ('s1','s2')
        /     \
       /       \
   ACCESS     ACCESS
    ('s1')    ('s2')
     |           |
   PROJECT    PROJECT
    ('s1')    ('s2')
     |           |
   SOURCE     SOURCE
    ('s1')    ('s2')
 

And after:

          ...
           |
        PROJECT ('s1','s2')      with the list of columns being SELECTed (from 's1' and 's2' selectors)
           |
        SELECT3 ('s1','s2')      Any SELECT plan nodes that apply to multiple selectors are left above
           |                     the ACCESS nodes.
         JOIN ('s1','s2')
        /     \
       /       \
   ACCESS     ACCESS
   ('s1')     ('s2')
     |           |
  PROJECT     PROJECT
   ('s1')     ('s2')
     |           |
  SELECT1     SELECT2
   ('s1')     ('s2')
     |           |
  SELECT4     SOURCE
   ('s1')     ('s2')
     |
   SOURCE
   ('s1')
 

Also, any SELECT that applies to one side of an equi-join will be applied to both sides of the JOIN.

Field Summary

Fields

Modifier and Type	Field and Description
static PushSelectCriteria	INSTANCE

Constructor Summary

Constructors

Constructor and Description
PushSelectCriteria()

Method Summary

Modifier and Type	Method and Description
protected boolean	atBoundary(PlanNode criteriaNode, PlanNode originatingNode) Determine whether all of the nodes between the criteria node and its originating node are criteria (SELECT) nodes.
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 PlanNode	findBestChildForCriteria(PlanNode criteriaNode, PlanNode originatingNode)
protected PlanNode	findOriginatingNode(PlanNode criteriaNode, List<PlanNode> originatingNodes) Find the first node that has all of the same selectors as the supplied criteria.
protected boolean	pushDownJoinCriteria(PlanNode criteriaNode, PlanNode joinNode) Attempt to push down criteria that applies to the JOIN as additional constraints on the JOIN itself.
protected boolean	pushTowardsOriginatingNode(PlanNode criteriaNode, PlanNode originatingNode) Push the criteria node as close to the originating node as possible.
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 PushSelectCriteria INSTANCE

Constructor Detail

PushSelectCriteria

public PushSelectCriteria()

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

pushDownJoinCriteria

protected boolean pushDownJoinCriteria(PlanNode criteriaNode,
                                       PlanNode joinNode)

Attempt to push down criteria that applies to the JOIN as additional constraints on the JOIN itself.

Parameters:

criteriaNode - the SELECT node; may not be null

joinNode - the JOIN node; may not be null

Returns:

true if the criteria was pushed down, or false otherwise

findOriginatingNode

protected PlanNode findOriginatingNode(PlanNode criteriaNode,
                                       List<PlanNode> originatingNodes)

Find the first node that has all of the same selectors as the supplied criteria.

Parameters:

criteriaNode - the criteria

originatingNodes - the list of nodes to search

Returns:

the first (highest) node that is uses all of the same selectors as the criteria, or null if no such node could be found

pushTowardsOriginatingNode

protected boolean pushTowardsOriginatingNode(PlanNode criteriaNode,
                                             PlanNode originatingNode)

Push the criteria node as close to the originating node as possible. In general, the criteria node usually ends up being moved to be a parent of the supplied originating node, except in a couple of cases:

• There are already criteria nodes immediately above the originating node; in this case, the supplied criteria node is placed above all these existing criteria nodes.
• The originating node is below a JOIN node that is itself below an ACCESS node; in this case, the criteria node is placed immediately above the JOIN node.
• The originating node is below a LIMIT with a single SORT child node; in this case, the criteria node is placed immediately above the LIMIT node.

Parameters:

criteriaNode - the criteria node that is to be pushed down; may not be null

originatingNode - the target node that represents the node above which the criteria node should be inserted; may not be null

Returns:

true if the criteria node was pushed down, or false if the criteria node could not be pushed down

findBestChildForCriteria

protected PlanNode findBestChildForCriteria(PlanNode criteriaNode,
                                            PlanNode originatingNode)

atBoundary

protected boolean atBoundary(PlanNode criteriaNode,
                             PlanNode originatingNode)

Determine whether all of the nodes between the criteria node and its originating node are criteria (SELECT) nodes.

Parameters:

criteriaNode - the criteria node; may not be null

originatingNode - the originating node

Returns:

true if all nodes between the criteria and originating nodes are SELECT nodes

toString

public String toString()

Overrides:

toString in class Object