org.apache.hadoop.hive.ql.optimizer.SetHashGroupByMinReduction Maven / Gradle / Ivy
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package org.apache.hadoop.hive.ql.optimizer;
import java.util.ArrayList;
import java.util.List;
import java.util.Stack;
import org.apache.hadoop.hive.ql.exec.ColumnInfo;
import org.apache.hadoop.hive.ql.exec.GroupByOperator;
import org.apache.hadoop.hive.ql.lib.Node;
import org.apache.hadoop.hive.ql.lib.SemanticNodeProcessor;
import org.apache.hadoop.hive.ql.lib.NodeProcessorCtx;
import org.apache.hadoop.hive.ql.parse.SemanticException;
import org.apache.hadoop.hive.ql.plan.ColStatistics;
import org.apache.hadoop.hive.ql.plan.GroupByDesc;
import org.apache.hadoop.hive.ql.plan.GroupByDesc.Mode;
import org.apache.hadoop.hive.ql.plan.Statistics;
import org.apache.hadoop.hive.ql.plan.Statistics.State;
import org.apache.hadoop.hive.ql.stats.StatsUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* SetHashGroupByMinReduction determines the min reduction to perform
* a hash aggregation for a group by.
*/
public class SetHashGroupByMinReduction implements SemanticNodeProcessor {
private static final Logger LOG = LoggerFactory.getLogger(SetHashGroupByMinReduction.class.getName());
@SuppressWarnings("unchecked")
@Override
public Object process(Node nd, Stack stack,
NodeProcessorCtx procContext, Object... nodeOutputs)
throws SemanticException {
GroupByOperator groupByOperator = (GroupByOperator) nd;
GroupByDesc desc = groupByOperator.getConf();
if (desc.getMode() != Mode.HASH || groupByOperator.getStatistics().getBasicStatsState() != State.COMPLETE
|| groupByOperator.getStatistics().getColumnStatsState() != State.COMPLETE) {
return null;
}
// compute product of distinct values of grouping columns
List colStats = new ArrayList<>();
for (int i = 0; i < desc.getKeys().size(); i++) {
ColumnInfo ci = groupByOperator.getSchema().getSignature().get(i);
colStats.add(
groupByOperator.getStatistics().getColumnStatisticsFromColName(ci.getInternalName()));
}
Statistics parentStats = groupByOperator.getParentOperators().get(0).getStatistics();
long ndvProduct = StatsUtils.computeNDVGroupingColumns(
colStats, parentStats, true);
// if ndvProduct is 0 then column stats state must be partial and we are missing
if (ndvProduct == 0) {
return null;
}
long numRows = parentStats.getNumRows();
if (ndvProduct > numRows) {
ndvProduct = numRows;
}
// change the min reduction for hash group by
float defaultMinReductionHashAggrFactor = desc.getMinReductionHashAggr();
float defaultMinReductionHashAggrFactorLowerBound = desc.getMinReductionHashAggrLowerBound();
float minReductionHashAggrFactor = 1f - ((float) ndvProduct / numRows);
if (minReductionHashAggrFactor < defaultMinReductionHashAggrFactorLowerBound) {
minReductionHashAggrFactor = defaultMinReductionHashAggrFactorLowerBound;
}
if (minReductionHashAggrFactor < defaultMinReductionHashAggrFactor) {
desc.setMinReductionHashAggr(minReductionHashAggrFactor);
if (LOG.isDebugEnabled()) {
LOG.debug("Minimum reduction for hash group by operator {} set to {}", groupByOperator, minReductionHashAggrFactor);
}
}
return null;
}
}