/* This file is part of VoltDB.
* Copyright (C) 2008-2014 VoltDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with VoltDB. If not, see <http://www.gnu.org/licenses/>.
*/
package org.voltdb.plannodes;
import java.util.List;
import org.voltdb.catalog.Cluster;
import org.voltdb.catalog.Database;
import org.voltdb.catalog.Table;
import org.voltdb.compiler.DatabaseEstimates;
import org.voltdb.compiler.DatabaseEstimates.TableEstimates;
import org.voltdb.compiler.ScalarValueHints;
import org.voltdb.planner.parseinfo.StmtTableScan;
import org.voltdb.planner.parseinfo.StmtTargetTableScan;
import org.voltdb.types.PlanNodeType;
public class SeqScanPlanNode extends AbstractScanPlanNode {
public SeqScanPlanNode() {
super();
}
public SeqScanPlanNode(StmtTableScan tableScan) {
setTableScan(tableScan);
}
public SeqScanPlanNode(String tableName, String tableAlias) {
super(tableName, tableAlias);
assert(tableName != null && tableAlias != null);
}
public static SeqScanPlanNode createDummyForTest(String tableName,
List<SchemaColumn> scanColumns) {
SeqScanPlanNode result = new SeqScanPlanNode(tableName, tableName);
result.setScanColumns(scanColumns);
return result;
}
@Override
public PlanNodeType getPlanNodeType() {
return PlanNodeType.SEQSCAN;
}
/**
* Accessor for flag marking the plan as guaranteeing an identical result/effect
* when "replayed" against the same database state, such as during replication or CL recovery.
* @return false
*/
@Override
public boolean isOrderDeterministic() {
return false; // TODO: enhance to return true for any supportable cases of in-order storage
}
private static final TableEstimates SUBQUERY_TABLE_ESTIMATES_HACK = new TableEstimates();
@Override
public void computeCostEstimates(long childOutputTupleCountEstimate, Cluster cluster, Database db, DatabaseEstimates estimates, ScalarValueHints[] paramHints) {
if (m_isSubQuery) {
// Get estimates from the sub-query
// @TODO For the sub-query the cost estimates will be calculated separately
// At the moment its contribution to the parent's cost plan is irrelevant because
// all parent plans have the same best cost plan for the sub-query
m_estimatedProcessedTupleCount = SUBQUERY_TABLE_ESTIMATES_HACK.minTuples;
m_estimatedOutputTupleCount = SUBQUERY_TABLE_ESTIMATES_HACK.minTuples;
return;
}
Table target = ((StmtTargetTableScan)m_tableScan).getTargetTable();
TableEstimates tableEstimates = estimates.getEstimatesForTable(target.getTypeName());
// This maxTuples value estimates the number of tuples fetched from the sequential scan.
// It's a vague measure of the cost of the scan.
// Its accuracy depends a lot on what kind of post-filtering or projection needs to happen, if any.
// The tuplesRead value is also used to estimate the number of RESULT rows, regardless of
// how effective post-filtering might be -- as if all rows passed the filters.
// This is at least semi-consistent with the ignoring of post-filter effects in IndexScanPlanNode.
// In effect, though, it gives index scans an "unfair" advantage when they reduce the estimated result size
// by taking into account the indexed filters -- follow-on plan steps, sorts (etc.), are costed lower
// as if they are operating on fewer rows than would have come out of the seqscan,
// though that's nonsense.
// In any case, it's important to keep an eye on any changes (discounts) to SeqScanPlanNode's costing
// here to make sure that SeqScanPlanNode never gains an unfair advantage over IndexScanPlanNode.
m_estimatedProcessedTupleCount = tableEstimates.maxTuples;
m_estimatedOutputTupleCount = tableEstimates.maxTuples;
}
@Override
public void resolveColumnIndexes() {
if (m_isSubQuery) {
assert(m_children.size() == 1);
m_children.get(0).resolveColumnIndexes();
}
super.resolveColumnIndexes();
}
@Override
protected String explainPlanForNode(String indent) {
String tableName = m_targetTableName == null? m_targetTableAlias: m_targetTableName;
return "SEQUENTIAL SCAN of \"" + tableName + "\"" + explainPredicate("\n" + indent + " filter by ");
}
}