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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>
98 lines
3.6 KiB
XML
98 lines
3.6 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!--
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Licensed to the Apache Software Foundation (ASF) under one
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or more contributor license agreements. See the NOTICE file
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distributed with this work for additional information
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regarding copyright ownership. The ASF licenses this file
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to you under the Apache License, Version 2.0 (the
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"License"); you may not use this file except in compliance
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with the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing,
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software distributed under the License is distributed on an
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"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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KIND, either express or implied. See the License for the
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specific language governing permissions and limitations
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under the License.
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-->
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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
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<concept id="default_spillable_buffer_size" rev="2.10.0 IMPALA-3200">
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<title>DEFAULT_SPILLABLE_BUFFER_SIZE Query Option</title>
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<titlealts audience="PDF"><navtitle>DEFAULT SPILLABLE BUFFER SIZE</navtitle></titlealts>
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<prolog>
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<metadata>
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<data name="Category" value="Impala"/>
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<data name="Category" value="Impala Query Options"/>
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<data name="Category" value="Querying"/>
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<data name="Category" value="Developers"/>
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<data name="Category" value="Data Analysts"/>
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</metadata>
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</prolog>
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<conbody>
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<p>
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<indexterm audience="hidden">DEFAULT_SPILLABLE_BUFFER_SIZE query option</indexterm>
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Specifies the default size for a memory buffer used when the
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spill-to-disk mechanism is activated, for example for queries against
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a large table with no statistics, or large join operations.
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</p>
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<p conref="../shared/impala_common.xml#common/type_integer"/>
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<!-- DEFAULT_SPILLABLE_BUFFER_SIZE: [2097152] -->
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<p conref="../shared/impala_common.xml#common/default_blurb"/>
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<p>
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<codeph>2097152</codeph> (2 MB)
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</p>
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<p conref="../shared/impala_common.xml#common/units_blurb"/>
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<p conref="../shared/impala_common.xml#common/added_in_2100"/>
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<p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>
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<p>
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This query option sets an upper bound on the size of the internal
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buffer size that can be used during spill-to-disk operations. The
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actual size of the buffer is chosen by the query planner.
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</p>
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<p>
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If overall query performance is limited by the time needed for spilling,
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consider increasing the <codeph>DEFAULT_SPILLABLE_BUFFER_SIZE</codeph> setting.
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Larger buffer sizes result in Impala issuing larger I/O requests to storage
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devices, which might result in higher throughput, particularly on rotational
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disks.
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</p>
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<p>
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The tradeoff with a large value for this setting is increased memory usage during
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spill-to-disk operations. Reducing this value may reduce memory consumption.
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</p>
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<p>
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To determine if the value for this setting is having an effect by capping the
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spillable buffer size, you can see the buffer size chosen by the query planner for
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a particular query. <codeph>EXPLAIN</codeph> the query while the setting
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<codeph>EXPLAIN_LEVEL=2</codeph> is in effect.
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</p>
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<p conref="../shared/impala_common.xml#common/example_blurb"/>
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<codeblock><![CDATA[
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set default_spillable_buffer_size=4MB;
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]]>
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</codeblock>
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<p conref="../shared/impala_common.xml#common/related_info"/>
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<p>
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<xref keyref="buffer_pool_limit"/>,
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<xref keyref="max_row_size"/>,
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<xref keyref="min_spillable_buffer_size"/>,
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<xref keyref="scalability_buffer_pool"/>
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</p>
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</conbody>
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</concept>
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