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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>
118 lines
3.6 KiB
XML
118 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="parquet_read_statistics">
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<title>PARQUET_READ_STATISTICS Query Option (<keyword keyref="impala29"/> or higher only)</title>
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<titlealts audience="PDF">
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<navtitle>PARQUET READ STATISTICS</navtitle>
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</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="Parquet"/>
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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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The <codeph>PARQUET_READ_STATISTICS</codeph> query option controls whether to read
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statistics from Parquet files and use them during query processing.
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</p>
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<p>
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Parquet stores min/max stats which can be used to skip reading row groups if they don't
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qualify a certain predicate. When this query option is set to <codeph>true</codeph>,
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Impala reads the Parquet statistics and skips reading row groups that do not match the
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conditions in the <codeph>WHERE</codeph> clause.
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</p>
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<p>
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Impala supports filtering based on Parquet statistics:
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</p>
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<ul>
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<li>
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Of the numerical types for the old version of the statistics: Boolean, Integer, Float
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</li>
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<li>
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Of the types for the new version of the statistics (starting in IMPALA 2.8): Boolean,
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Integer, Float, Decimal, String, Timestamp
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</li>
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<li>
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For simple predicates of the forms: <codeph><slot> <op> <constant></codeph> or
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<codeph><constant> <op> <slot></codeph>, where <codeph><op></codeph> is LT,
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LE, GE, GT, and EQ
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</li>
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</ul>
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<p>
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The <codeph>PARQUET_READ_STATISTICS</codeph> option provides a workaround when dealing
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with files that have corrupt Parquet statistics and unknown errors.
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</p>
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<p>
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In the query runtime profile output for each Impalad instance, the
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<codeph>NumStatsFilteredRowGroups</codeph> field in the SCAN node section shows the number
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of row groups that were skipped based on Parquet statistics.
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</p>
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<p>
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The supported values for the query option are:
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<ul>
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<li>
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<codeph>true</codeph> (<codeph>1</codeph>): Read statistics from Parquet files and use
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them in query processing.
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</li>
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<li>
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<codeph>false</codeph> (<codeph>0</codeph>): Do not use Parquet read statistics.
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</li>
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<li>
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Any other values are treated as <codeph>false</codeph>.
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</li>
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</ul>
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</p>
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<p>
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<b>Type:</b> Boolean
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</p>
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<p>
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<b>Default:</b> <codeph>true</codeph>
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</p>
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<p conref="../shared/impala_common.xml#common/added_in_290"/>
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</conbody>
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</concept>
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