/**
* 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.drill.exec.planner.physical;
import java.io.IOException;
import java.util.Iterator;
import java.util.List;
import org.apache.drill.exec.physical.base.PhysicalOperator;
import org.apache.drill.exec.physical.config.TopN;
import org.apache.drill.exec.planner.cost.DrillCostBase;
import org.apache.drill.exec.planner.cost.DrillCostBase.DrillCostFactory;
import org.apache.drill.exec.record.BatchSchema.SelectionVectorMode;
import org.eigenbase.rel.RelCollation;
import org.eigenbase.rel.RelNode;
import org.eigenbase.rel.RelWriter;
import org.eigenbase.rel.SingleRel;
import org.eigenbase.rel.metadata.RelMetadataQuery;
import org.eigenbase.relopt.RelOptCluster;
import org.eigenbase.relopt.RelOptCost;
import org.eigenbase.relopt.RelOptPlanner;
import org.eigenbase.relopt.RelTraitSet;
import org.eigenbase.rex.RexLiteral;
import org.eigenbase.rex.RexNode;
public class TopNPrel extends SinglePrel {
protected int limit;
protected final RelCollation collation;
public TopNPrel(RelOptCluster cluster, RelTraitSet traitSet, RelNode child, int limit, RelCollation collation) {
super(cluster, traitSet, child);
this.limit = limit;
this.collation = collation;
}
@Override
public RelNode copy(RelTraitSet traitSet, List<RelNode> inputs) {
return new TopNPrel(getCluster(), traitSet, sole(inputs), this.limit, this.collation);
}
@Override
public PhysicalOperator getPhysicalOperator(PhysicalPlanCreator creator) throws IOException {
Prel child = (Prel) this.getChild();
PhysicalOperator childPOP = child.getPhysicalOperator(creator);
TopN topN = new TopN(childPOP, PrelUtil.getOrdering(this.collation, getChild().getRowType()), false, this.limit);
return creator.addMetadata(this, topN);
}
/**
* Cost of doing Top-N is proportional to M log N where M is the total number of
* input rows and N is the limit for Top-N. This makes Top-N preferable to Sort
* since cost of full Sort is proportional to M log M .
*/
@Override
public RelOptCost computeSelfCost(RelOptPlanner planner) {
if(PrelUtil.getSettings(getCluster()).useDefaultCosting()) {
//We use multiplier 0.05 for TopN operator, and 0.1 for Sort, to make TopN a preferred choice.
return super.computeSelfCost(planner).multiplyBy(0.05);
}
RelNode child = this.getChild();
double inputRows = RelMetadataQuery.getRowCount(child);
int numSortFields = this.collation.getFieldCollations().size();
double cpuCost = DrillCostBase.COMPARE_CPU_COST * numSortFields * inputRows * (Math.log(limit)/Math.log(2));
double diskIOCost = 0; // assume in-memory for now until we enforce operator-level memory constraints
DrillCostFactory costFactory = (DrillCostFactory)planner.getCostFactory();
return costFactory.makeCost(inputRows, cpuCost, diskIOCost, 0);
}
@Override
public RelWriter explainTerms(RelWriter pw) {
return super.explainTerms(pw)
.item("limit", limit);
}
@Override
public SelectionVectorMode[] getSupportedEncodings() {
return SelectionVectorMode.NONE_AND_TWO;
}
@Override
public SelectionVectorMode getEncoding() {
return SelectionVectorMode.FOUR_BYTE;
}
}