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* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.apache.pig.newplan.optimizer;
import java.util.ArrayList;
import java.util.List;
import java.util.Set;
import org.apache.pig.impl.logicalLayer.FrontendException;
import org.apache.pig.newplan.OperatorPlan;
/**
* The core class of the optimizer. The basic design of this class is that it
* is provided a list of RuleSets. RuleSets represent all of the optimizer
* rules that can be run together. The rules in the RuleSet will be run
* repeatedly until either no rule in the RuleSet passes check and calls
* transform or until maxIter iterations (default 500) has been made over
* the RuleSet. Then the next RuleSet will be moved to. Once finished,
* a given RuleSet is never returned to.
*
* Each rule is has two parts: a pattern and and associated transformer.
* Transformers have two important functions: check(), and transform().
* The pattern describes a pattern of node types that the optimizer will
* look to match. If that match is found anywhere in the plan, then check()
* will be called. check() allows the rule to look more in depth at the
* matched pattern and decide whether the rule should be run or not. For
* example, one might design a rule to push filters above join that would
* look for the pattern filter(join) (meaning a filter followed by a join).
* But only certain types of filters can be pushed. The check() function
* would need to decide whether the filter that it found was pushable or not.
* If check() returns true, the rule is said to have matched, and transform()
* is then called. This function is responsible for making changes in the
* logical plan. Once transform is complete PlanPatcher.patchUp will be
* called to do any necessary cleanup in the plan, such as resetting
* schemas, etc.
*/
public abstract class PlanOptimizer {
protected List<Set<Rule>> ruleSets;
protected OperatorPlan plan;
protected List<PlanTransformListener> listeners;
protected int maxIter;
static final int defaultIterations = 500;
/**
* @param p Plan to optimize
* @param rs List of RuleSets to use to optimize
* @param iterations maximum number of optimization iterations,
* set to -1 for default
*/
protected PlanOptimizer(OperatorPlan p,
List<Set<Rule>> rs,
int iterations) {
plan = p;
ruleSets = rs;
listeners = new ArrayList<PlanTransformListener>();
maxIter = (iterations < 1 ? defaultIterations : iterations);
}
/**
* Adds a listener to the optimization. This listener will be fired
* after each rule transforms a plan. Listeners are guaranteed to
* be fired in the order they are added.
* @param listener
*/
protected void addPlanTransformListener(PlanTransformListener listener) {
listeners.add(listener);
}
/**
* Run the optimizer. This method attempts to match each of the Rules
* against the plan. If a Rule matches, it then calls the check
* method of the associated Transformer to give the it a chance to
* check whether it really wants to do the optimization. If that
* returns true as well, then Transformer.transform is called.
* @throws FrontendException
*/
public void optimize() throws FrontendException {
for (Set<Rule> rs : ruleSets) {
boolean sawMatch = false;
int numIterations = 0;
do {
sawMatch = false;
for (Rule rule : rs) {
List<OperatorPlan> matches = rule.match(plan);
if (matches != null) {
Transformer transformer = rule.getNewTransformer();
for (OperatorPlan m : matches) {
try {
if (transformer.check(m)) {
sawMatch = true;
transformer.transform(m);
if (!rule.isSkipListener()) {
for(PlanTransformListener l: listeners) {
l.transformed(plan, transformer.reportChanges());
}
}
}
} catch (Exception e) {
StringBuffer message = new StringBuffer("Error processing rule " + rule.name);
if (!rule.isMandatory()) {
message.append(". Try -t " + rule.name);
}
throw new FrontendException(message.toString(), 2000, e);
}
}
}
}
} while(sawMatch && ++numIterations < maxIter);
}
}
}