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From jacques-n <...@git.apache.org>
Subject [GitHub] drill pull request: DRILL-3623: Use shorter query path for LIMIT 0...
Date Tue, 17 Nov 2015 17:28:15 GMT
Github user jacques-n commented on a diff in the pull request:

    https://github.com/apache/drill/pull/193#discussion_r45090426
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/planner/logical/DrillDirectScanRel.java
---
    @@ -0,0 +1,111 @@
    +/**
    + * 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.logical;
    +
    +import com.google.common.collect.Iterators;
    +import org.apache.calcite.plan.RelOptCluster;
    +import org.apache.calcite.plan.RelTraitSet;
    +import org.apache.calcite.rel.AbstractRelNode;
    +import org.apache.calcite.rel.RelWriter;
    +import org.apache.calcite.rel.type.RelDataType;
    +import org.apache.drill.common.logical.data.LogicalOperator;
    +import org.apache.drill.exec.physical.base.PhysicalOperator;
    +import org.apache.drill.exec.planner.physical.DrillScanPrel;
    +import org.apache.drill.exec.planner.physical.PhysicalPlanCreator;
    +import org.apache.drill.exec.planner.physical.PlannerSettings;
    +import org.apache.drill.exec.planner.physical.Prel;
    +import org.apache.drill.exec.planner.physical.PrelUtil;
    +import org.apache.drill.exec.planner.physical.visitor.PrelVisitor;
    +import org.apache.drill.exec.record.BatchSchema;
    +import org.apache.drill.exec.store.direct.DirectGroupScan;
    +
    +import java.io.IOException;
    +import java.util.Iterator;
    +
    +/**
    + * Logical and physical RelNode representing a {@link DirectGroupScan}. This is not backed
by a {@link DrillTable},
    + * unlike {@link DrillScanRel}.
    + */
    +public class DrillDirectScanRel extends AbstractRelNode implements DrillScanPrel, DrillRel
{
    --- End diff --
    
    There is one challenge with the Values execution in Drill. We use data to encode types
(and generate the vectors). It seems like the ideal would be expressing a values operation
that has no data. Maybe we should just support a local limit in the values operator? That
would allow us to bypass adding the limit(0) and sv remover for the simple case. Generally,
we should probably support leaf node limit pushdown anyway. I see the new patch takes a different
approach to the one above. One of the things that seemed to be an issue above is that the
Limit operator was properly terminating its parents in the fast schema case of a limit 0.
@sudheeshkatkam and @jinfengni, do you agree that is an issue? If it is, we should get a JIRA
opened for it.


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