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* ModeShape (http://www.modeshape.org)
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.modeshape.jcr.query.optimize;
import java.util.Collections;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Set;
import org.modeshape.common.annotation.Immutable;
import org.modeshape.jcr.query.QueryContext;
import org.modeshape.jcr.query.model.Column;
import org.modeshape.jcr.query.model.Constraint;
import org.modeshape.jcr.query.model.EquiJoinCondition;
import org.modeshape.jcr.query.model.JoinCondition;
import org.modeshape.jcr.query.model.PropertyExistence;
import org.modeshape.jcr.query.model.PropertyValue;
import org.modeshape.jcr.query.model.ReferenceValue;
import org.modeshape.jcr.query.model.SelectorName;
import org.modeshape.jcr.query.model.Visitable;
import org.modeshape.jcr.query.model.Visitors;
import org.modeshape.jcr.query.model.Visitors.AbstractVisitor;
import org.modeshape.jcr.query.plan.PlanNode;
import org.modeshape.jcr.query.plan.PlanNode.Property;
import org.modeshape.jcr.query.plan.PlanNode.Type;
import org.modeshape.jcr.query.plan.PlanUtil;
/**
* An {@link OptimizerRule optimizer rule} that moves up higher in the plan any SELECT node that appears below a JOIN node and
* that applies to selectors that are on the other side of the join.
* <p>
* This step is often counterintuitive, since one of the best optimizations a query optimizer can do is to
* {@link PushSelectCriteria push down SELECT nodes} as far as they'll go. But consider the case of a SOURCE node that appears
* below a JOIN, where the SOURCE node is a view. The optimizer {@link ReplaceViews replaces the SOURCE node with the view
* definition}, and if the view definition includes a SELECT node, that SELECT node appears below the JOIN. Plus, that SELECT node
* is already pushed down as far as it can go (assuming the view isn't defined to use another view). However, the JOIN may use the
* same selector on the opposite side, and it may be possible that the same SELECT node may apply to the other side of the JOIN.
* In this case, we can push <i>up</i> the SELECT node higher than the JOIN, and then the push-down would cause the SELECT to be
* copied to both sides of the JOIN.
* </p>
* <p>
* Here is an example plan that involves a JOIN of two SOURCE nodes:
*
* <pre>
* ...
* |
* JOIN
* / \
* / SOURCE({@link Property#SOURCE_NAME SOURCE_NAME}="t1")
* /
* SOURCE({@link Property#SOURCE_NAME SOURCE_NAME}="v1")
* </pre>
*
* If the right-side SOURCE references the "t1" table, and the left-side SOURCE references a view "v1" defined as "
* <code>SELECT * FROM t1 WHERE t1.id < 3</code>", then the {@link ReplaceViews} rule would change this plan to be:
*
* <pre>
* ...
* |
* JOIN
* / \
* / SOURCE({@link Property#SOURCE_NAME SOURCE_NAME}="t1")
* /
* PROJECT
* |
* SELECT applies the "t1.id < 3" criteria
* |
* SOURCE({@link Property#SOURCE_NAME SOURCE_NAME}="t1")
* </pre>
*
* Again, the SELECT cannot be pushed down any further. But the whole query can be made more efficient - because the SELECT on the
* left-side of the JOIN will include only those tuples from 't1' that satisfy the SELECT, the JOIN will only include those tuples
* that also satisfy this criteria, even though more tuples are returned from the right-side SOURCE.
* </p>
* <p>
* In this case, the left-hand SELECT can actually be copied to the right-hand side of the JOIN, resulting in:
*
* <pre>
* ...
* |
* JOIN
* / \
* / SELECT applies the "t1.id < 3" criteria
* / |
* PROJECT SOURCE({@link Property#SOURCE_NAME SOURCE_NAME}="t1")
* |
* SELECT applies the "t1.id < 3" criteria
* |
* SOURCE({@link Property#SOURCE_NAME SOURCE_NAME}="t1")
* </pre>
*
* </p>
*/
@Immutable
public class RaiseSelectCriteria implements OptimizerRule {
public static final RaiseSelectCriteria INSTANCE = new RaiseSelectCriteria();
@Override
public PlanNode execute( QueryContext context,
PlanNode plan,
LinkedList<OptimizerRule> ruleStack ) {
Set<PlanNode> copiedSelectNodes = new HashSet<PlanNode>();
for (PlanNode join : plan.findAllAtOrBelow(Type.JOIN)) {
// Get the join condition ...
JoinCondition joinCondition = join.getProperty(Property.JOIN_CONDITION, JoinCondition.class);
if (joinCondition instanceof EquiJoinCondition) {
EquiJoinCondition equiJoinCondition = (EquiJoinCondition)joinCondition;
SelectorName selector1 = equiJoinCondition.selector1Name();
SelectorName selector2 = equiJoinCondition.selector2Name();
String property1 = equiJoinCondition.getProperty1Name();
String property2 = equiJoinCondition.getProperty2Name();
// Walk up the tree looking for SELECT nodes that apply to one of the sides ...
PlanNode node = join.getParent();
while (node != null) {
if (!copiedSelectNodes.contains(node)) {
PlanNode copy = copySelectNode(context, node, selector1, property1, selector2, property2);
if (copy != null) {
node.insertAsParent(copy);
copiedSelectNodes.add(node);
copiedSelectNodes.add(copy);
} else {
copy = copySelectNode(context, node, selector2, property2, selector1, property1);
if (copy != null) {
node.insertAsParent(copy);
copiedSelectNodes.add(node);
copiedSelectNodes.add(copy);
}
}
}
node = node.getParent();
}
}
}
return plan;
}
protected PlanNode copySelectNode( QueryContext context,
PlanNode selectNode,
SelectorName selectorName,
String propertyName,
SelectorName copySelectorName,
String copyPropertyName ) {
if (selectNode.isNot(Type.SELECT)) return null;
if (selectNode.getSelectors().size() != 1 || !selectNode.getSelectors().contains(selectorName)) return null;
Constraint constraint = selectNode.getProperty(Property.SELECT_CRITERIA, Constraint.class);
Set<Column> columns = getColumnsReferencedBy(constraint);
if (columns.size() != 1) return null;
Column column = columns.iterator().next();
if (!column.selectorName().equals(selectorName)) return null;
if (!column.getPropertyName().equals(propertyName)) return null;
// We know that this constraint ONLY applies to the referenced selector and property,
// so we will duplicate this constraint ...
// Create the new node ...
PlanNode copy = new PlanNode(Type.SELECT, copySelectorName);
// Copy the constraint, but change the references to the copy selector and property ...
PlanUtil.ColumnMapping mappings = new PlanUtil.ColumnMapping(selectorName);
mappings.map(propertyName, new Column(copySelectorName, copyPropertyName, copyPropertyName));
Constraint newCriteria = PlanUtil.replaceReferences(context, constraint, mappings, copy);
copy.setProperty(Property.SELECT_CRITERIA, newCriteria);
return copy;
}
@Override
public String toString() {
return getClass().getSimpleName();
}
/**
* Get the set of Column objects that represent those columns referenced by the visitable object.
*
* @param visitable the object to be visited
* @return the set of Column objects, with column names that always are the string-form of the {@link Column#getPropertyName()
* property name}; never null
*/
public static Set<Column> getColumnsReferencedBy( Visitable visitable ) {
if (visitable == null) return Collections.emptySet();
final Set<Column> symbols = new HashSet<Column>();
// Walk the entire structure, so only supply a StrategyVisitor (that does no navigation) ...
Visitors.visitAll(visitable, new AbstractVisitor() {
protected void addColumnFor( SelectorName selectorName,
String property ) {
symbols.add(new Column(selectorName, property, property));
}
@Override
public void visit( Column column ) {
symbols.add(column);
}
@Override
public void visit( EquiJoinCondition joinCondition ) {
addColumnFor(joinCondition.selector1Name(), joinCondition.getProperty1Name());
addColumnFor(joinCondition.selector2Name(), joinCondition.getProperty2Name());
}
@Override
public void visit( PropertyExistence prop ) {
addColumnFor(prop.selectorName(), prop.getPropertyName());
}
@Override
public void visit( PropertyValue prop ) {
addColumnFor(prop.selectorName(), prop.getPropertyName());
}
@Override
public void visit( ReferenceValue ref ) {
String propertyName = ref.getPropertyName();
if (propertyName != null) {
addColumnFor(ref.selectorName(), propertyName);
}
}
});
return symbols;
}
}