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These are refugees from doc_prototype. They can be rendered with the DITA Open Toolkit version 2.3.3 by: /tmp/dita-ot-2.3.3/bin/dita \ -i impala.ditamap \ -f html5 \ -o $(mktemp -d) \ -filter impala_html.ditaval Change-Id: I8861e99adc446f659a04463ca78c79200669484f Reviewed-on: http://gerrit.cloudera.org:8080/5014 Reviewed-by: John Russell <jrussell@cloudera.com> Tested-by: John Russell <jrussell@cloudera.com>
99 lines
3.3 KiB
XML
99 lines
3.3 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
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<concept rev="2.0.0" id="compression_codec">
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<title>COMPRESSION_CODEC Query Option (<keyword keyref="impala20"/> or higher only)</title>
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<titlealts audience="PDF"><navtitle>COMPRESSION_CODEC</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="Compression"/>
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<data name="Category" value="File Formats"/>
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<data name="Category" value="Parquet"/>
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<data name="Category" value="Snappy"/>
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<data name="Category" value="Gzip"/>
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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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<!-- The initial part of this paragraph is copied straight from the #parquet_compression topic. -->
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<!-- Could turn into a conref. -->
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<p rev="2.0.0">
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<indexterm audience="Cloudera">COMPRESSION_CODEC query option</indexterm>
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When Impala writes Parquet data files using the <codeph>INSERT</codeph> statement, the underlying compression
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is controlled by the <codeph>COMPRESSION_CODEC</codeph> query option.
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</p>
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<note>
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Prior to Impala 2.0, this option was named <codeph>PARQUET_COMPRESSION_CODEC</codeph>. In Impala 2.0 and
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later, the <codeph>PARQUET_COMPRESSION_CODEC</codeph> name is not recognized. Use the more general name
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<codeph>COMPRESSION_CODEC</codeph> for new code.
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</note>
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<p conref="../shared/impala_common.xml#common/syntax_blurb"/>
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<codeblock>SET COMPRESSION_CODEC=<varname>codec_name</varname>;</codeblock>
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<p>
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The allowed values for this query option are <codeph>SNAPPY</codeph> (the default), <codeph>GZIP</codeph>,
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and <codeph>NONE</codeph>.
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</p>
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<note>
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A Parquet file created with <codeph>COMPRESSION_CODEC=NONE</codeph> is still typically smaller than the
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original data, due to encoding schemes such as run-length encoding and dictionary encoding that are applied
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separately from compression.
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</note>
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<p></p>
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<p>
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The option value is not case-sensitive.
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</p>
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<p>
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If the option is set to an unrecognized value, all kinds of queries will fail due to the invalid option
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setting, not just queries involving Parquet tables. (The value <codeph>BZIP2</codeph> is also recognized, but
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is not compatible with Parquet tables.)
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</p>
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<p>
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<b>Type:</b> <codeph>STRING</codeph>
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</p>
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<p>
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<b>Default:</b> <codeph>SNAPPY</codeph>
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</p>
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<p conref="../shared/impala_common.xml#common/example_blurb"/>
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<codeblock>set compression_codec=gzip;
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insert into parquet_table_highly_compressed select * from t1;
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set compression_codec=snappy;
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insert into parquet_table_compression_plus_fast_queries select * from t1;
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set compression_codec=none;
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insert into parquet_table_no_compression select * from t1;
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set compression_codec=foo;
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select * from t1 limit 5;
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ERROR: Invalid compression codec: foo
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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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For information about how compressing Parquet data files affects query performance, see
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<xref href="impala_parquet.xml#parquet_compression"/>.
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</p>
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</conbody>
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</concept>
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