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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.hadoop.hive.ql.optimizer;
import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.Map;
import org.apache.hadoop.hive.ql.exec.CommonJoinOperator;
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.LateralViewForwardOperator;
import org.apache.hadoop.hive.ql.exec.LateralViewJoinOperator;
import org.apache.hadoop.hive.ql.exec.LimitOperator;
import org.apache.hadoop.hive.ql.exec.MapJoinOperator;
import org.apache.hadoop.hive.ql.exec.PTFOperator;
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.parse.ParseContext;
import org.apache.hadoop.hive.ql.parse.SemanticException;
/**
* Implementation of one of the rule-based optimization steps. ColumnPruner gets
* the current operator tree. The \ tree is traversed to find out the columns
* used for all the base tables. If all the columns for a table are not used, a
* select is pushed on top of that table (to select only those columns). Since
* this changes the row resolver, the tree is built again. This can be optimized
* later to patch the tree.
*/
public class ColumnPruner implements Transform {
protected ParseContext pGraphContext;
/**
* empty constructor.
*/
public ColumnPruner() {
pGraphContext = null;
}
/**
* Transform the query tree. For each table under consideration, check if all
* columns are needed. If not, only select the operators needed at the
* beginning and proceed.
*
* @param pactx
* the current parse context
*/
@Override
public ParseContext transform(ParseContext pactx) throws SemanticException {
pGraphContext = pactx;
// generate pruned column list for all relevant operators
ColumnPrunerProcCtx cppCtx = new ColumnPrunerProcCtx(pactx);
// 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 opRules = new LinkedHashMap();
opRules.put(new RuleRegExp("R1",
FilterOperator.getOperatorName() + "%"),
ColumnPrunerProcFactory.getFilterProc());
opRules.put(new RuleRegExp("R2",
GroupByOperator.getOperatorName() + "%"),
ColumnPrunerProcFactory.getGroupByProc());
opRules.put(new RuleRegExp("R3",
ReduceSinkOperator.getOperatorName() + "%"),
ColumnPrunerProcFactory.getReduceSinkProc());
opRules.put(new RuleRegExp("R4",
SelectOperator.getOperatorName() + "%"),
ColumnPrunerProcFactory.getSelectProc());
opRules.put(new RuleRegExp("R5",
CommonJoinOperator.getOperatorName() + "%"),
ColumnPrunerProcFactory.getJoinProc());
opRules.put(new RuleRegExp("R6",
MapJoinOperator.getOperatorName() + "%"),
ColumnPrunerProcFactory.getMapJoinProc());
opRules.put(new RuleRegExp("R7",
TableScanOperator.getOperatorName() + "%"),
ColumnPrunerProcFactory.getTableScanProc());
opRules.put(new RuleRegExp("R8",
LateralViewJoinOperator.getOperatorName() + "%"),
ColumnPrunerProcFactory.getLateralViewJoinProc());
opRules.put(new RuleRegExp("R9",
LateralViewForwardOperator.getOperatorName() + "%"),
ColumnPrunerProcFactory.getLateralViewForwardProc());
opRules.put(new RuleRegExp("R10",
PTFOperator.getOperatorName() + "%"),
ColumnPrunerProcFactory.getPTFProc());
opRules.put(new RuleRegExp("R11",
ScriptOperator.getOperatorName() + "%"),
ColumnPrunerProcFactory.getScriptProc());
opRules.put(new RuleRegExp("R12",
LimitOperator.getOperatorName() + "%"),
ColumnPrunerProcFactory.getLimitProc());
// The dispatcher fires the processor corresponding to the closest matching
// rule and passes the context along
Dispatcher disp = new DefaultRuleDispatcher(ColumnPrunerProcFactory
.getDefaultProc(), opRules, cppCtx);
GraphWalker ogw = new ColumnPrunerWalker(disp);
// Create a list of topop nodes
ArrayList topNodes = new ArrayList();
topNodes.addAll(pGraphContext.getTopOps().values());
ogw.startWalking(topNodes, null);
return pGraphContext;
}
/**
* Walks the op tree in post order fashion (skips selects with file sink or
* script op children).
*/
public static class ColumnPrunerWalker extends DefaultGraphWalker {
public ColumnPrunerWalker(Dispatcher disp) {
super(disp);
}
/**
* Walk the given operator.
*/
@Override
public void walk(Node nd) throws SemanticException {
boolean walkChildren = true;
opStack.push(nd);
// no need to go further down for a select op with a file sink or script
// child
// since all cols are needed for these ops
if (nd instanceof SelectOperator) {
for (Node child : nd.getChildren()) {
if ((child instanceof FileSinkOperator)
|| (child instanceof ScriptOperator)) {
walkChildren = false;
}
}
}
if ((nd.getChildren() == null)
|| getDispatchedList().containsAll(nd.getChildren()) || !walkChildren) {
// all children are done or no need to walk the children
dispatch(nd, opStack);
opStack.pop();
return;
}
// move all the children to the front of queue
getToWalk().removeAll(nd.getChildren());
getToWalk().addAll(0, nd.getChildren());
// add self to the end of the queue
getToWalk().add(nd);
opStack.pop();
}
}
}
