/**
* 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.hadoop.hive.ql.optimizer;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.hadoop.hive.ql.exec.FileSinkOperator;
import org.apache.hadoop.hive.ql.exec.FilterOperator;
import org.apache.hadoop.hive.ql.exec.GroupByOperator;
import org.apache.hadoop.hive.ql.exec.JoinOperator;
import org.apache.hadoop.hive.ql.exec.Operator;
import org.apache.hadoop.hive.ql.exec.ReduceSinkOperator;
import org.apache.hadoop.hive.ql.exec.ScriptOperator;
import org.apache.hadoop.hive.ql.exec.SelectOperator;
import org.apache.hadoop.hive.ql.exec.TableScanOperator;
import org.apache.hadoop.hive.ql.lib.DefaultGraphWalker;
import org.apache.hadoop.hive.ql.lib.DefaultRuleDispatcher;
import org.apache.hadoop.hive.ql.lib.Dispatcher;
import org.apache.hadoop.hive.ql.lib.GraphWalker;
import org.apache.hadoop.hive.ql.lib.Node;
import org.apache.hadoop.hive.ql.lib.NodeProcessor;
import org.apache.hadoop.hive.ql.lib.Rule;
import org.apache.hadoop.hive.ql.lib.RuleRegExp;
import org.apache.hadoop.hive.ql.optimizer.ConstantPropagateProcCtx.ConstantPropagateOption;
import org.apache.hadoop.hive.ql.parse.ParseContext;
import org.apache.hadoop.hive.ql.parse.SemanticException;
/**
* Implementation of one of the rule-based optimization steps. ConstantPropagate traverse the DAG
* from root to child. For each conditional expression, process as follows:
*
* 1. Fold constant expression: if the expression is a UDF and all parameters are constant.
*
* 2. Shortcut expression: if the expression is a logical operator and it can be shortcut by
* some constants of its parameters.
*
* 3. Propagate expression: if the expression is an assignment like column=constant, the expression
* will be propagate to parents to see if further folding operation is possible.
*/
public class ConstantPropagate extends Transform {
private static final Logger LOG = LoggerFactory.getLogger(ConstantPropagate.class);
protected ParseContext pGraphContext;
private ConstantPropagateOption constantPropagateOption;
public ConstantPropagate() {
this(ConstantPropagateOption.FULL);
}
public ConstantPropagate(ConstantPropagateOption option) {
this.constantPropagateOption = option;
}
/**
* Transform the query tree.
*
* @param pactx
* the current parse context
*/
@Override
public ParseContext transform(ParseContext pactx) throws SemanticException {
pGraphContext = pactx;
// generate pruned column list for all relevant operators
ConstantPropagateProcCtx cppCtx = new ConstantPropagateProcCtx(constantPropagateOption);
// create a walker which walks the tree in a DFS manner while maintaining
// the operator stack. The dispatcher
// generates the plan from the operator tree
Map<Rule, NodeProcessor> opRules = new LinkedHashMap<Rule, NodeProcessor>();
opRules.put(new RuleRegExp("R1", FilterOperator.getOperatorName() + "%"),
ConstantPropagateProcFactory.getFilterProc());
opRules.put(new RuleRegExp("R2", GroupByOperator.getOperatorName() + "%"),
ConstantPropagateProcFactory.getGroupByProc());
opRules.put(new RuleRegExp("R3", SelectOperator.getOperatorName() + "%"),
ConstantPropagateProcFactory.getSelectProc());
opRules.put(new RuleRegExp("R4", FileSinkOperator.getOperatorName() + "%"),
ConstantPropagateProcFactory.getFileSinkProc());
opRules.put(new RuleRegExp("R5", ReduceSinkOperator.getOperatorName() + "%"),
ConstantPropagateProcFactory.getReduceSinkProc());
opRules.put(new RuleRegExp("R6", JoinOperator.getOperatorName() + "%"),
ConstantPropagateProcFactory.getJoinProc());
opRules.put(new RuleRegExp("R7", TableScanOperator.getOperatorName() + "%"),
ConstantPropagateProcFactory.getTableScanProc());
opRules.put(new RuleRegExp("R8", ScriptOperator.getOperatorName() + "%"),
ConstantPropagateProcFactory.getStopProc());
// The dispatcher fires the processor corresponding to the closest matching
// rule and passes the context along
Dispatcher disp = new DefaultRuleDispatcher(ConstantPropagateProcFactory
.getDefaultProc(), opRules, cppCtx);
GraphWalker ogw = new ConstantPropagateWalker(disp);
// Create a list of operator nodes to start the walking.
ArrayList<Node> topNodes = new ArrayList<Node>();
topNodes.addAll(pGraphContext.getTopOps().values());
ogw.startWalking(topNodes, null);
for (Operator<? extends Serializable> opToDelete : cppCtx.getOpToDelete()) {
if (opToDelete.getParentOperators() == null || opToDelete.getParentOperators().size() != 1) {
throw new RuntimeException("Error pruning operator " + opToDelete
+ ". It should have only 1 parent.");
}
opToDelete.getParentOperators().get(0).removeChildAndAdoptItsChildren(opToDelete);
}
cppCtx.getOpToDelete().clear();
return pGraphContext;
}
/**
* Walks the op tree in root first order.
*/
public static class ConstantPropagateWalker extends DefaultGraphWalker {
public ConstantPropagateWalker(Dispatcher disp) {
super(disp);
}
@Override
protected void walk(Node nd) throws SemanticException {
List<Node> parents = ((Operator) nd).getParentOperators();
if ((parents == null)
|| getDispatchedList().containsAll(parents)) {
opStack.push(nd);
// all children are done or no need to walk the children
dispatch(nd, opStack);
opStack.pop();
} else {
toWalk.removeAll(parents);
toWalk.add(0, nd);
toWalk.addAll(0, parents);
return;
}
// move all the children to the front of queue
List<? extends Node> children = nd.getChildren();
if (children != null) {
toWalk.removeAll(children);
toWalk.addAll(children);
}
}
}
}