mirror of
https://github.com/apache/impala.git
synced 2025-12-19 09:58:28 -05:00
eadd35f6d5
The recent documentation formatting changes introduced the navigation panel on the left. However, due to the length of the query options navigation title these could overlap with the documentation paragraphs. This commit removes the underscores from the navigation titles of the query options, so browsers can break them into multiple lines. Additionally, the "SET" and "Query Options for the SET Statement" pages are merged to save some more space for the query option navigation titles. Testing: - Built the documentation and tested manually Change-Id: Icec787d7a2af848aaaff65be2ecf311a5ce8fe7f Reviewed-on: http://gerrit.cloudera.org:8080/20556 Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com> Reviewed-by: Jason Fehr <jfehr@cloudera.com> Reviewed-by: Peter Rozsa <prozsa@cloudera.com> Reviewed-by: Tamas Mate <tmater@apache.org>
81 lines
2.8 KiB
XML
81 lines
2.8 KiB
XML
<?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
|
|
|
|
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.
|
|
-->
|
|
<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
|
|
<concept id="schedule_random_replica" rev="2.5.0">
|
|
|
|
<title>SCHEDULE_RANDOM_REPLICA Query Option (<keyword keyref="impala25"/> or higher only)</title>
|
|
|
|
<titlealts audience="PDF">
|
|
|
|
<navtitle>SCHEDULE RANDOM REPLICA</navtitle>
|
|
|
|
</titlealts>
|
|
|
|
<prolog>
|
|
<metadata>
|
|
<data name="Category" value="Impala"/>
|
|
<data name="Category" value="Impala Query Options"/>
|
|
<data name="Category" value="Performance"/>
|
|
<data name="Category" value="Developers"/>
|
|
<data name="Category" value="Data Analysts"/>
|
|
</metadata>
|
|
</prolog>
|
|
|
|
<conbody>
|
|
|
|
<p>
|
|
The <codeph>SCHEDULE_RANDOM_REPLICA</codeph> query option fine-tunes the scheduling
|
|
algorithm for deciding which host processes each HDFS data block or Kudu tablet to reduce
|
|
the chance of CPU hotspots.
|
|
</p>
|
|
|
|
<p>
|
|
By default, Impala estimates how much work each host has done for the query, and selects
|
|
the host that has the lowest workload. This algorithm is intended to reduce CPU hotspots
|
|
arising when the same host is selected to process multiple data blocks / tablets. Use the
|
|
<codeph>SCHEDULE_RANDOM_REPLICA</codeph> query option if hotspots still arise for some
|
|
combinations of queries and data layout.
|
|
</p>
|
|
|
|
<p>
|
|
The <codeph>SCHEDULE_RANDOM_REPLICA</codeph> query option only applies to tables and
|
|
partitions that are not enabled for the HDFS caching.
|
|
</p>
|
|
|
|
<p conref="../shared/impala_common.xml#common/type_boolean"/>
|
|
|
|
<p conref="../shared/impala_common.xml#common/default_false"/>
|
|
|
|
<p conref="../shared/impala_common.xml#common/added_in_250"/>
|
|
|
|
<p conref="../shared/impala_common.xml#common/related_info"/>
|
|
|
|
<p>
|
|
<xref href="impala_perf_hdfs_caching.xml#hdfs_caching"/>,
|
|
<xref
|
|
href="impala_scalability.xml#scalability_hotspots"/> ,
|
|
<xref
|
|
href="impala_replica_preference.xml#replica_preference"/>
|
|
</p>
|
|
|
|
</conbody>
|
|
|
|
</concept>
|