UnassignedScanSingleRemoteTableJob.java

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package org.apache.doris.nereids.trees.plans.distribute.worker.job;

import org.apache.doris.nereids.StatementContext;
import org.apache.doris.nereids.trees.plans.distribute.DistributeContext;
import org.apache.doris.nereids.trees.plans.distribute.worker.DistributedPlanWorker;
import org.apache.doris.nereids.trees.plans.distribute.worker.DistributedPlanWorkerManager;
import org.apache.doris.nereids.trees.plans.distribute.worker.ScanWorkerSelector;
import org.apache.doris.planner.ExchangeNode;
import org.apache.doris.planner.PlanFragment;
import org.apache.doris.planner.ScanNode;
import org.apache.doris.thrift.TPushAggOp;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ListMultimap;

import java.util.List;
import java.util.Map;
import java.util.Objects;

/**
 * UnassignedScanSingleRemoteTableJob
 * it should be a leaf job which not contains scan native olap table node,
 * for example, select literal without table, or scan an external table
 */
public class UnassignedScanSingleRemoteTableJob extends AbstractUnassignedScanJob {
    private final ScanWorkerSelector scanWorkerSelector;

    public UnassignedScanSingleRemoteTableJob(
            StatementContext statementContext, PlanFragment fragment, ScanNode scanNode,
            ListMultimap<ExchangeNode, UnassignedJob> exchangeToChildJob, ScanWorkerSelector scanWorkerSelector) {
        super(statementContext, fragment, ImmutableList.of(scanNode), exchangeToChildJob);
        this.scanWorkerSelector = Objects.requireNonNull(scanWorkerSelector, "scanWorkerSelector is not null");
    }

    /**
     * Select a worker for each scan range of the external / remote table scan node.
     * For external tables (Hive, Iceberg, etc.), scan ranges represent file splits
     * rather than tablets, and workers are selected based on data locality or
     * workload balancing.
     *
     * @param distributeContext the distribute context
     * @param inputJobs multimap from child exchange nodes to their assigned jobs
     * @return a map from worker to its assigned file scan ranges
     */
    @Override
    protected Map<DistributedPlanWorker, UninstancedScanSource> multipleMachinesParallelization(
            DistributeContext distributeContext, ListMultimap<ExchangeNode, AssignedJob> inputJobs) {
        return scanWorkerSelector.selectReplicaAndWorkerWithoutBucket(
                scanNodes.get(0), statementContext.getConnectContext()
        );
    }

    /**
     * A COUNT pushdown over one file split does not benefit from creating local
     * shuffle instances: the scanner already produces the complete scalar
     * result.  In particular, the local-shuffle path otherwise uses the
     * fragment parallelism and can create many empty scan instances.  Apply
     * this restriction only after ranges have been selected, and only when this
     * worker has one assigned range for the COUNT case. Other aggregates,
     * multi-split scans and non-file remote scans retain the base
     * parallelization rules.
     */
    @Override
    protected int degreeOfParallelism(int maxParallel, boolean useLocalShuffleToAddParallel) {
        int instanceNum = super.degreeOfParallelism(maxParallel, useLocalShuffleToAddParallel);
        ScanNode scanNode = scanNodes.get(0);
        if (scanNode.getPushDownAggNoGroupingOp() == TPushAggOp.COUNT && maxParallel == 1) {
            return 1;
        }
        return instanceNum;
    }

    /**
     * If all file scan ranges have been pruned and the assigned job list is empty,
     * create a single empty instance on a random worker so the fragment can still
     * execute (returning an empty result) rather than failing.
     *
     * @param assignedJobs the list produced by {@link #insideMachineParallelization}
     * @param workerManager the worker manager to select a fallback worker from
     * @param inputJobs multimap from child exchange nodes to their assigned jobs
     * @return the original list if non-empty, otherwise a single empty instance
     */
    @Override
    protected List<AssignedJob> fillUpAssignedJobs(List<AssignedJob> assignedJobs,
            DistributedPlanWorkerManager workerManager, ListMultimap<ExchangeNode, AssignedJob> inputJobs) {
        if (assignedJobs.isEmpty()) {
            // the file scan have pruned, so no assignedJobs,
            // we should allocate an instance of it,
            assignedJobs = fillUpSingleEmptyInstance(workerManager);
        }
        return assignedJobs;
    }
}