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6a2c9049ff
Clarify comment about # of DataNodes. Change-Id: I662a59a59da8a170a2710d4a5245363ae1e3f754 Reviewed-on: http://gerrit.cloudera.org:8080/5651 Reviewed-by: Tim Armstrong <tarmstrong@cloudera.com> Tested-by: Impala Public Jenkins
101 lines
3.2 KiB
XML
101 lines
3.2 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 rev="IMPALA-3671" id="scratch_limit">
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<title>SCRATCH_LIMIT Query Option</title>
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<titlealts audience="PDF"><navtitle>SCRATCH_LIMIT</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="Memory"/>
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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">SCRATCH_LIMIT query option</indexterm>
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Specifies the maximum amount of disk storage, in bytes, that any Impala query can consume
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on any host using the <q>spill to disk</q> mechanism that handles queries that exceed
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the memory limit.
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</p>
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<p conref="../shared/impala_common.xml#common/syntax_blurb"/>
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<p>
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Specify the size in bytes, or with a trailing <codeph>m</codeph> or <codeph>g</codeph> character to indicate
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megabytes or gigabytes. For example:
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</p>
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<!-- Examples adapted from impala_parquet_file_size.xml.
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To do: demonstrate with queries that succeed / fail
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based on the query option setting, and interaction
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with MEM_LIMIT. -->
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<codeblock>-- 128 megabytes.
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set SCRATCH_LIMIT=134217728
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-- 512 megabytes.
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set SCRATCH_LIMIT=512m;
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-- 1 gigabyte.
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set SCRATCH_LIMIT=1g;
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</codeblock>
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<p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>
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<p>
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A value of zero turns off the spill to disk feature for queries
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in the current session, causing them to fail immediately if they
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exceed the memory limit.
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</p>
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<p>
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The amount of memory used per host for a query is limited by the
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<codeph>MEM_LIMIT</codeph> query option.
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</p>
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<p>
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The more Impala daemon hosts in the cluster, the less memory is used on each host,
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and therefore also less scratch space is required for queries that
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exceed the memory limit.
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</p>
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<p>
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<b>Type:</b> numeric, with optional unit specifier
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</p>
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<p>
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<b>Default:</b> -1 (amount of spill space is unlimited)
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</p>
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<p conref="../shared/impala_common.xml#common/related_info"/>
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<p>
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<xref href="impala_scalability.xml#spill_to_disk"/>,
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<xref href="impala_mem_limit.xml#mem_limit"/>
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</p>
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</conbody>
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</concept>
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