mirror of
https://github.com/apache/impala.git
synced 2025-12-30 03:01:44 -05:00
9073402f20
Change-Id: I8ecbf93749d5eb8da1d5c873fd7503f5bb2c7d0f Reviewed-on: http://gerrit.cloudera.org:8080/10733 Reviewed-by: Alex Rodoni <arodoni@cloudera.com> Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>
96 lines
3.9 KiB
XML
96 lines
3.9 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 rev="2.10.0" id="disable_codegen_rows_threshold">
|
|
|
|
<title>DISABLE_CODEGEN_ROWS_THRESHOLD Query Option (<keyword keyref="impala210_full"/> or higher only)</title>
|
|
<titlealts audience="PDF"><navtitle>DISABLE_CODEGEN_ROWS_THRESHOLD</navtitle></titlealts>
|
|
<prolog>
|
|
<metadata>
|
|
<data name="Category" value="Impala"/>
|
|
<data name="Category" value="Impala Query Options"/>
|
|
<data name="Category" value="Scalability"/>
|
|
<data name="Category" value="Performance"/>
|
|
<data name="Category" value="Developers"/>
|
|
<data name="Category" value="Data Analysts"/>
|
|
</metadata>
|
|
</prolog>
|
|
|
|
<conbody>
|
|
|
|
<p rev="2.0.0"> This setting controls the cutoff point (in terms of number
|
|
of rows processed per Impala daemon) below which Impala disables native
|
|
code generation for the whole query. Native code generation is very
|
|
beneficial for queries that process many rows because it reduces the time
|
|
taken to process of each row. However, generating the native code adds
|
|
latency to query startup. Therefore, automatically disabling codegen for
|
|
queries that process relatively small amounts of data can improve query
|
|
response time. </p>
|
|
|
|
<p conref="../shared/impala_common.xml#common/syntax_blurb"/>
|
|
|
|
<codeblock>SET DISABLE_CODEGEN_ROWS_THRESHOLD=<varname>number_of_rows</varname></codeblock>
|
|
|
|
<p>
|
|
<b>Type:</b> numeric
|
|
</p>
|
|
|
|
<p>
|
|
<b>Default:</b> 50000
|
|
</p>
|
|
|
|
<p>
|
|
<b>Usage notes:</b> Typically, you increase the default value to make this optimization apply to more queries.
|
|
If incorrect or corrupted table and column statistics cause Impala to apply this optimization incorrectly to
|
|
queries that actually involve substantial work, you might see the queries being slower as a result of codegen
|
|
being disabled. In that case, recompute statistics with the <codeph>COMPUTE STATS</codeph> or
|
|
<codeph>COMPUTE INCREMENTAL STATS</codeph> statement. If there is a problem collecting accurate statistics,
|
|
you can turn this feature off by setting the value to 0.
|
|
</p>
|
|
|
|
<p conref="../shared/impala_common.xml#common/internals_blurb"/>
|
|
|
|
<p>
|
|
This setting applies to queries where the number of rows processed can be accurately
|
|
determined, either through table and column statistics, or by the presence of a
|
|
<codeph>LIMIT</codeph> clause. If Impala cannot accurately estimate the number of rows,
|
|
then this setting does not apply.
|
|
</p>
|
|
|
|
<p rev="2.3.0">
|
|
If a query uses the complex data types <codeph>STRUCT</codeph>, <codeph>ARRAY</codeph>,
|
|
or <codeph>MAP</codeph>, then codegen is never automatically disabled regardless of the
|
|
<codeph>DISABLE_CODEGEN_ROWS_THRESHOLD</codeph> setting.
|
|
</p>
|
|
|
|
<p conref="../shared/impala_common.xml#common/added_in_2100"/>
|
|
|
|
<!-- Don't have any other places that tie into this particular optimization technique yet.
|
|
Potentially: conceptual topics about code generation, distributed queries
|
|
|
|
<p conref="../shared/impala_common.xml#common/related_info"/>
|
|
<p>
|
|
</p>
|
|
-->
|
|
|
|
</conbody>
|
|
|
|
</concept>
|