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8377b9949c
For this change to land in master, the audience="hidden" code review needs to be completed first. Otherwise, the doc build would still work but the audience="hidden" content would be visible rather than hidden as desired. Some work happening in parallel might introduce additional instances of audience="Cloudera". I suggest addressing those in a followup CR so this global change can land quickly. Since the changes apply across so many different files, but are so narrow in scope, I suggest that the way to validate (check that no extraneous changes were introduced accidentally) is to diff just the changed lines: git diff -U0 HEAD^ HEAD In patch set 2, I updated other topics marked audience="Cloudera" by CRs that were pushed in the meantime. Change-Id: Ic93d89da77e1f51bbf548a522d98d0c4e2fb31c8 Reviewed-on: http://gerrit.cloudera.org:8080/5613 Reviewed-by: John Russell <jrussell@cloudera.com> Tested-by: Impala Public Jenkins
74 lines
2.7 KiB
XML
74 lines
2.7 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="max_scan_range_length">
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<title>MAX_SCAN_RANGE_LENGTH Query Option</title>
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<titlealts audience="PDF"><navtitle>MAX_SCAN_RANGE_LENGTH</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="Performance"/>
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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">MAX_SCAN_RANGE_LENGTH query option</indexterm>
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Maximum length of the scan range. Interacts with the number of HDFS blocks in the table to determine how many
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CPU cores across the cluster are involved with the processing for a query. (Each core processes one scan
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range.)
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</p>
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<p>
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Lowering the value can sometimes increase parallelism if you have unused CPU capacity, but a too-small value
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can limit query performance because each scan range involves extra overhead.
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</p>
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<p>
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Only applicable to HDFS tables. Has no effect on Parquet tables. Unspecified or 0 indicates backend default,
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which is the same as the HDFS block size for each table.
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</p>
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<p>
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Although the scan range can be arbitrarily long, Impala internally uses an 8 MB read buffer so that it can
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query tables with huge block sizes without allocating equivalent blocks of memory.
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</p>
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<p>
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<b>Type:</b> numeric
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</p>
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<p rev="IMPALA-3799 CDH-43746">
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In <keyword keyref="impala27_full"/> and higher, the argument value can include unit specifiers,
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such as <codeph>100m</codeph> or <codeph>100mb</codeph>. In previous versions,
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Impala interpreted such formatted values as 0, leading to query failures.
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</p>
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<p>
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<b>Default:</b> 0
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</p>
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</conbody>
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</concept>
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