blob: 804ca4faf26cdcb74f4c657b31aa2243f6f529e8 [file] [log] [blame]
<?xml version="1.0" encoding="UTF-8"?>
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
Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
KIND, either express or implied. See the License for the
specific language governing permissions and limitations
under the License.
<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="shuffle_distinct_exprs">
<title>SHUFFLE_DISTINCT_EXPRS Query Option</title>
<titlealts audience="PDF">
<data name="Category" value="Impala"/>
<data name="Category" value="Impala Query Options"/>
The <codeph>SHUFFLE_DISTINCT_EXPRS</codeph> query option controls the
shuffling behavior when a query has both grouping and distinct expressions.
Impala can optionally include the distinct expressions in the hash exchange
to spread the data among more nodes. However, this plan requires one more
hash exchange phase.
It is recommended that you turn off this option if the NDVs of the grouping
expressions are high.
<p conref="../shared/impala_common.xml#common/type_boolean"/>
<p conref="../shared/impala_common.xml#common/default_false"/>