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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-3623) Hive query hangs with limit 0 clause
Date Fri, 09 Oct 2015 13:40:27 GMT

    [ https://issues.apache.org/jira/browse/DRILL-3623?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14950396#comment-14950396

ASF GitHub Bot commented on DRILL-3623:

Github user jacques-n commented on a diff in the pull request:

    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/planner/sql/handlers/NonDeferredSchemaTableLimit0Visitor.java
    @@ -0,0 +1,126 @@
    + * 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
    + * <p/>
    + * http://www.apache.org/licenses/LICENSE-2.0
    + * <p/>
    + * 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.sql.handlers;
    +import com.google.common.collect.Lists;
    +import org.apache.calcite.rel.RelNode;
    +import org.apache.calcite.rel.RelShuttleImpl;
    +import org.apache.calcite.rel.core.TableScan;
    +import org.apache.calcite.rel.type.RelDataType;
    +import org.apache.calcite.sql.type.SqlTypeFactoryImpl;
    +import org.apache.calcite.sql.type.SqlTypeName;
    +import org.apache.drill.common.exceptions.ExecutionSetupException;
    +import org.apache.drill.common.expression.SchemaPath;
    +import org.apache.drill.common.types.TypeProtos;
    +import org.apache.drill.exec.exception.SchemaChangeException;
    +import org.apache.drill.exec.expr.TypeHelper;
    +import org.apache.drill.exec.ops.OperatorContext;
    +import org.apache.drill.exec.physical.impl.OutputMutator;
    +import org.apache.drill.exec.planner.logical.DrillConstExecutor;
    +import org.apache.drill.exec.planner.logical.DrillScanRel;
    +import org.apache.drill.exec.planner.logical.DrillTable;
    +import org.apache.drill.exec.planner.types.DrillRelDataTypeSystem;
    +import org.apache.drill.exec.record.MaterializedField;
    +import org.apache.drill.exec.store.AbstractRecordReader;
    +import org.apache.drill.exec.store.RecordReader;
    +import java.util.List;
    +import java.util.Map;
    + *
    + */
    +public class NonDeferredSchemaTableLimit0Visitor extends RelShuttleImpl {
    --- End diff --
    I think the logic here is incorrect/incomplete. We should be: 
    1. traverse the entire tree to determine if all the table leaves are FullySchemaed and
the root portion of the tree is limit 0. 
      - For schema detection, a better possibility would be to determine if the output is
fully schemaed as opposed to all the inputs are fully schemaed. Maybe this would work if we
verify that all of the fields of the root node are not an ANY type. @jinfengni could provide
comments here.
    2. If (1) is true, then we should read the schema of the root node of the tree
    3. Create a reader for the root node of the tree.
    The query here can be arbitrarily complex (many joins, group bys, etc).

> Hive query hangs with limit 0 clause
> ------------------------------------
>                 Key: DRILL-3623
>                 URL: https://issues.apache.org/jira/browse/DRILL-3623
>             Project: Apache Drill
>          Issue Type: Bug
>          Components: Storage - Hive
>    Affects Versions: 1.1.0
>         Environment: MapR cluster
>            Reporter: Andries Engelbrecht
>             Fix For: Future
> Running a select * from hive.table limit 0 does not return (hangs).
> Select * from hive.table limit 1 works fine
> Hive table is about 6GB with 330 files with parquet using snappy compression.
> Data types are int, bigint, string and double.
> Querying directory with parquet files through the DFS plugin works fine
> select * from dfs.root.`/user/hive/warehouse/database/table` limit 0;

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