docs/topics/impala_s3_skip_insert_staging.xml

<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="s3_skip_insert_staging" rev="2.6.0 IMPALA-3452">

  <title>S3_SKIP_INSERT_STAGING Query Option (<keyword keyref="impala26"/> or higher only)</title>
  <titlealts audience="PDF"><navtitle>S3_SKIP_INSERT_STAGING</navtitle></titlealts>
  <prolog>
    <metadata>
      <data name="Category" value="Impala"/>
      <data name="Category" value="Impala Query Options"/>
      <data name="Category" value="Amazon"/>
      <data name="Category" value="S3"/>
      <data name="Category" value="Performance"/>
      <data name="Category" value="Developers"/>
      <data name="Category" value="Data Analysts"/>
    </metadata>
  </prolog>

  <conbody>

    <p rev="2.6.0 IMPALA-3452">
      <indexterm audience="hidden">IMPALA_S3_SKIP_INSERT_STAGING query option</indexterm>
    </p>

    <p>
      Speeds up <codeph>INSERT</codeph> operations on tables or partitions residing on the
      Amazon S3 filesystem. The tradeoff is the possibility of inconsistent data left behind
      if an error occurs partway through the operation.
    </p>

    <p>
      By default, Impala write operations to S3 tables and partitions involve a two-stage process.
      Impala writes intermediate files to S3, then (because S3 does not provide a <q>rename</q>
      operation) those intermediate files are copied to their final location, making the process
      more expensive as on a filesystem that supports renaming or moving files.
      This query option makes Impala skip the intermediate files, and instead write the
      new data directly to the final destination.
    </p>

    <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>

    <note type="important">
      <p>
        If a host that is participating in the <codeph>INSERT</codeph> operation fails partway through
        the query, you might be left with a table or partition that contains some but not all of the
        expected data files. Therefore, this option is most appropriate for a development or test
        environment where you have the ability to reconstruct the table if a problem during
        <codeph>INSERT</codeph> leaves the data in an inconsistent state.
      </p>
    </note>

    <p>
      The timing of file deletion during an <codeph>INSERT OVERWRITE</codeph> operation
      makes it impractical to write new files to S3 and delete the old files in a single operation.
      Therefore, this query option only affects regular <codeph>INSERT</codeph> statements that add
      to the existing data in a table, not <codeph>INSERT OVERWRITE</codeph> statements.
      Use <codeph>TRUNCATE TABLE</codeph> if you need to remove all contents from an S3 table
      before performing a fast <codeph>INSERT</codeph> with this option enabled.
    </p>

    <p>
      Performance improvements with this option enabled can be substantial. The speed increase
      might be more noticeable for non-partitioned tables than for partitioned tables.
    </p>

    <p conref="../shared/impala_common.xml#common/type_boolean"/>
    <p conref="../shared/impala_common.xml#common/default_true_1"/>

    <p conref="../shared/impala_common.xml#common/added_in_260"/>

    <p conref="../shared/impala_common.xml#common/related_info"/>
    <p>
      <xref href="impala_s3.xml#s3"/>
    </p>

  </conbody>
</concept>