org.apache.hadoop.hive.ql.optimizer.physical.SamplingOptimizer Maven / Gradle / Ivy
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package org.apache.hadoop.hive.ql.optimizer.physical;
import org.apache.hadoop.hive.ql.exec.GroupByOperator;
import org.apache.hadoop.hive.ql.exec.Operator;
import org.apache.hadoop.hive.ql.exec.OperatorUtils;
import org.apache.hadoop.hive.ql.exec.ReduceSinkOperator;
import org.apache.hadoop.hive.ql.exec.TableScanOperator;
import org.apache.hadoop.hive.ql.exec.Task;
import org.apache.hadoop.hive.ql.exec.mr.MapRedTask;
import org.apache.hadoop.hive.ql.io.AcidUtils;
import org.apache.hadoop.hive.ql.metadata.Table;
import org.apache.hadoop.hive.ql.parse.SemanticException;
import org.apache.hadoop.hive.ql.plan.MapWork;
import org.apache.hadoop.hive.ql.plan.MapredWork;
import org.apache.hadoop.hive.ql.plan.ReduceWork;
/**
* Mark final MapredWork for ORDER BY to use sampling and set number of reduce task as -1
*/
public class SamplingOptimizer implements PhysicalPlanResolver {
public PhysicalContext resolve(PhysicalContext pctx) throws SemanticException {
for (Task task : pctx.getRootTasks()) {
if (!(task instanceof MapRedTask) || !((MapRedTask)task).getWork().isFinalMapRed()) {
continue; // this could be replaced by bucketing on RS + bucketed fetcher for next MR
}
MapredWork mrWork = ((MapRedTask) task).getWork();
MapWork mapWork = mrWork.getMapWork();
ReduceWork reduceWork = mrWork.getReduceWork();
if (reduceWork == null || reduceWork.getNumReduceTasks() != 1
|| mapWork.getAliasToWork().size() != 1 || mapWork.getSamplingType() > 0
|| reduceWork.getReducer() == null) {
continue;
}
// GROUPBY operator in reducer may not be processed in parallel. Skip optimizing.
if (OperatorUtils.findSingleOperator(reduceWork.getReducer(), GroupByOperator.class) != null) {
continue;
}
Operator operator = mapWork.getAliasToWork().values().iterator().next();
if (!(operator instanceof TableScanOperator)) {
continue;
}
TableScanOperator tsop = (TableScanOperator)operator;
Table tbl = tsop.getConf().getTableMetadata();
if (tbl == null) {
continue;
}
if (AcidUtils.isInsertOnlyTable(tbl.getParameters())) {
// Not supported for MM tables - sampler breaks separate MM dirs into splits, resulting in
// mismatch when the downstream task looks at them again assuming they are MM table roots.
// We could somehow unset the MM flag for the main job when the sampler succeeds, since the
// sampler will limit the input to the the correct directories, but we don't care about MR.
continue;
}
ReduceSinkOperator child =
OperatorUtils.findSingleOperator(operator, ReduceSinkOperator.class);
if (child == null ||
child.getConf().getNumReducers() != 1 || !child.getConf().getPartitionCols().isEmpty()) {
continue;
}
child.getConf().setNumReducers(-1);
reduceWork.setNumReduceTasks(-1);
mapWork.setSamplingType(MapWork.SAMPLING_ON_START);
}
return pctx;
}
}