/**
* 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.physical;
import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Stack;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.hive.ql.exec.FilterOperator;
import org.apache.hadoop.hive.ql.exec.LimitOperator;
import org.apache.hadoop.hive.ql.exec.TableScanOperator;
import org.apache.hadoop.hive.ql.lib.DefaultGraphWalker;
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.NodeProcessorCtx;
import org.apache.hadoop.hive.ql.lib.Rule;
import org.apache.hadoop.hive.ql.lib.RuleRegExp;
import org.apache.hadoop.hive.ql.optimizer.physical.MetadataOnlyOptimizer.WalkerCtx;
import org.apache.hadoop.hive.ql.parse.SemanticException;
import org.apache.hadoop.hive.ql.plan.ExprNodeConstantDesc;
import org.apache.hadoop.hive.ql.plan.ExprNodeDesc;
/**
* This optimizer attempts following two optimizations:
* 1. If it finds TS followed By FIL which has been determined at compile time to evaluate to
* zero, it removes all input paths for that table scan.
* 2. If it finds TS followed by Limit 0, it removes all input paths from table scan.
*/
public class NullScanOptimizer implements PhysicalPlanResolver {
private static final Log LOG = LogFactory.getLog(NullScanOptimizer.class.getName());
@Override
public PhysicalContext resolve(PhysicalContext pctx) throws SemanticException {
Map<Rule, NodeProcessor> opRules = new LinkedHashMap<Rule, NodeProcessor>();
opRules.put(new RuleRegExp("R1", TableScanOperator.getOperatorName() + "%.*" +
FilterOperator.getOperatorName() + "%"), new WhereFalseProcessor());
Dispatcher disp = new NullScanTaskDispatcher(pctx, opRules);
GraphWalker ogw = new DefaultGraphWalker(disp);
ArrayList<Node> topNodes = new ArrayList<Node>();
topNodes.addAll(pctx.getRootTasks());
ogw.startWalking(topNodes, null);
opRules.clear();
opRules.put(new RuleRegExp("R1", TableScanOperator.getOperatorName()+ "%"),new TSMarker());
opRules.put(new RuleRegExp("R2", LimitOperator.getOperatorName()+ "%"), new Limit0Processor());
disp = new NullScanTaskDispatcher(pctx, opRules);
ogw = new DefaultGraphWalker(disp);
topNodes = new ArrayList<Node>();
topNodes.addAll(pctx.getRootTasks());
ogw.startWalking(topNodes, null);
return pctx;
}
static private class WhereFalseProcessor implements NodeProcessor {
@Override
public Object process(Node nd, Stack<Node> stack, NodeProcessorCtx procCtx,
Object... nodeOutputs) throws SemanticException {
FilterOperator filter = (FilterOperator) nd;
ExprNodeDesc condition = filter.getConf().getPredicate();
if (!(condition instanceof ExprNodeConstantDesc)) {
return null;
}
ExprNodeConstantDesc c = (ExprNodeConstantDesc) condition;
if (!Boolean.FALSE.equals(c.getValue())) {
return null;
}
WalkerCtx ctx = (WalkerCtx) procCtx;
for (Node op : stack) {
if (op instanceof TableScanOperator) {
ctx.setMayBeMetadataOnly((TableScanOperator)op);
LOG.info("Found where false TableScan. " + op);
}
}
ctx.convertMetadataOnly();
return null;
}
}
static private class Limit0Processor implements NodeProcessor {
@Override
public Object process(Node nd, Stack<Node> stack, NodeProcessorCtx procCtx,
Object... nodeOutputs) throws SemanticException {
if(!(((LimitOperator)nd).getConf().getLimit() == 0)) {
return null;
}
LOG.info("Found Limit 0 TableScan. " + nd);
((WalkerCtx)procCtx).convertMetadataOnly();
return null;
}
}
static private class TSMarker implements NodeProcessor {
@Override
public Object process(Node nd, Stack<Node> stack, NodeProcessorCtx procCtx,
Object... nodeOutputs) throws SemanticException {
((WalkerCtx)procCtx).setMayBeMetadataOnly((TableScanOperator)nd);
return null;
}
}
}