mirror of
https://github.com/apache/impala.git
synced 2026-02-03 09:00:39 -05:00
2d74dfd5e2
Change-Id: Id131b66a3457ef6cbc326a0f3ed99de2a3950c3e Reviewed-on: http://gerrit.cloudera.org:8080/14394 Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com> Reviewed-by: Quanlong Huang <huangquanlong@gmail.com>
90 lines
2.9 KiB
XML
90 lines
2.9 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="disable_hbase_num_rows_estimate">
|
|
|
|
<title>DISABLE_HBASE_NUM_ROWS_ESTIMATE Query Option</title>
|
|
|
|
<titlealts audience="PDF">
|
|
|
|
<navtitle>DISABLE_HBASE_NUM_ROWS_ESTIMATE</navtitle>
|
|
|
|
</titlealts>
|
|
|
|
<prolog>
|
|
<metadata>
|
|
<data name="Category" value="Impala"/>
|
|
<data name="Category" value="Impala Query Options"/>
|
|
<data name="Category" value="Performance"/>
|
|
</metadata>
|
|
</prolog>
|
|
|
|
<conbody>
|
|
|
|
<p>
|
|
Use the <codeph>DISABLE_HBASE_NUM_ROWS_ESTIMATE</codeph> query option to disable key
|
|
sampling of HBase tables in row count and row size estimation.
|
|
</p>
|
|
|
|
<p>
|
|
While generating a plan for an HBase query, the planner samples the underlying HBase
|
|
tables to estimate their row count and row size, and the sampling can negatively impact
|
|
the planning time. When the HBase table stats does not change much in short time, disable
|
|
the sampling by setting the <codeph>DISABLE_HBASE_NUM_ROWS_ESTIMATE</codeph> query option
|
|
to <codeph>TRUE</codeph>. And Impala planner will fall back to using Hive Metastore (HMS)
|
|
table stats instead.
|
|
</p>
|
|
|
|
<p>
|
|
When <codeph>DISABLE_HBASE_NUM_ROWS_ESTIMATE</codeph> query option is set to
|
|
<codeph>TRUE</codeph>, you need to update the HMS table stats by running <codeph>COMPUTE
|
|
STATS</codeph>. Alternatively, you can manually set table statistics by running
|
|
<codeph>ALTER TABLE</codeph>. See <xref
|
|
href="impala_perf_stats.xml#perf_stats"/>
|
|
for details.
|
|
</p>
|
|
|
|
<p>
|
|
The following values are supported:
|
|
<ul>
|
|
<li>
|
|
<codeph>TRUE</codeph> or <codeph>1</codeph>: Disables the normal key sampling of HBase
|
|
tables and uses HMS table stats for estimation.
|
|
</li>
|
|
|
|
<li>
|
|
<codeph>FALSE</codeph> or <codeph>0</codeph>: Enables the normal sampling of HBase
|
|
tables.
|
|
</li>
|
|
</ul>
|
|
</p>
|
|
|
|
<p>
|
|
<b>Type:</b> <codeph>BOOLEAN</codeph>
|
|
</p>
|
|
|
|
<p>
|
|
<b>Default:</b> <codeph>FALSE</codeph>
|
|
</p>
|
|
|
|
</conbody>
|
|
|
|
</concept>
|