impala/docs/topics/impala_refresh.xml

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

  <title>REFRESH Statement</title>

  <titlealts audience="PDF">

    <navtitle>REFRESH</navtitle>

  </titlealts>

  <prolog>
    <metadata>
      <data name="Category" value="Impala"/>
      <data name="Category" value="SQL"/>
      <data name="Category" value="DDL"/>
      <data name="Category" value="Tables"/>
      <data name="Category" value="Hive"/>
      <data name="Category" value="Metastore"/>
      <data name="Category" value="ETL"/>
      <data name="Category" value="Ingest"/>
      <data name="Category" value="Developers"/>
      <data name="Category" value="Data Analysts"/>
    </metadata>
  </prolog>

  <conbody>

    <p>
      The <codeph>REFRESH</codeph> statement reloads the metadata for the table from the
      metastore database and does an incremental reload of the file and block metadata from the
      HDFS NameNode. <codeph>REFRESH</codeph> is used to avoid inconsistencies between Impala
      and external metadata sources, namely Hive Metastore (HMS) and NameNodes.
    </p>

    <p> The <codeph>REFRESH</codeph> statement is only required if you load data
      from outside of Impala. Updated metadata, as a result of running
        <codeph>REFRESH</codeph>, is broadcast to all Impala coordinators. </p>

    <p>
      See <xref href="impala_hadoop.xml#intro_metastore"/> for the information about the way
      Impala uses metadata and how it shares the same metastore database as Hive.
    </p>

    <p>
      Once issued, the <codeph>REFRESH</codeph> statement cannot be cancelled.
    </p>

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

<codeblock rev="IMPALA-1683">REFRESH [<varname>db_name</varname>.]<varname>table_name</varname> [PARTITION (<varname>key_col1</varname>=<varname>val1</varname> [, <varname>key_col2</varname>=<varname>val2</varname>...])]</codeblock>

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

    <p>
      The table name is a required parameter, and the table must already exist and be known to
      Impala.
    </p>

    <p>
      Only the metadata for the specified table is reloaded.
    </p>

    <p>
      Use the <codeph>REFRESH</codeph> statement to load the latest metastore metadata for a
      particular table after one of the following scenarios happens outside of Impala:
    </p>

    <ul>
      <li> Deleting, adding, or modifying files. <p> For example, after loading
          new data files into the HDFS data directory for the table, appending
          to an existing HDFS file, inserting data from Hive via
            <codeph>INSERT</codeph> or <codeph>LOAD DATA</codeph>. </p>
      </li>

      <li>
        Deleting, adding, or modifying partitions.
        <p>
          For example, after issuing <codeph>ALTER TABLE</codeph> or other table-modifying SQL
          statement in Hive
        </p>
      </li>
    </ul>

    <note rev="2.3.0">
      <p rev="2.3.0">
        In <keyword keyref="impala23_full"/> and higher, the <codeph>ALTER TABLE
        <varname>table_name</varname> RECOVER PARTITIONS</codeph> statement is a faster
        alternative to <codeph>REFRESH</codeph> when you are only adding new partition
        directories through Hive or manual HDFS operations. See
        <xref
          href="impala_alter_table.xml#alter_table"/> for details.
      </p>
    </note>

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

    <p rev="IMPALA-1683">
      <b>Refreshing a single partition:</b>
    </p>

    <p rev="IMPALA-1683">
      In <keyword keyref="impala27_full"/> and higher, the <codeph>REFRESH</codeph> statement
      can apply to a single partition at a time, rather than the whole table. Include the
      optional <codeph>PARTITION (<varname>partition_spec</varname>)</codeph> clause and specify
      values for each of the partition key columns.
    </p>

    <p>
      The following rules apply:
      <ul>
        <li>
          The <codeph>PARTITION</codeph> clause of the <codeph>REFRESH</codeph> statement must
          include all the partition key columns.
        </li>

        <li>
          The order of the partition key columns does not have to match the column order in the
          table.
        </li>

        <li>
          Specifying a nonexistent partition does not cause an error.
        </li>

        <li>
          The partition can be one that Impala created and is already aware of, or a new
          partition created through Hive.
        </li>
      </ul>
    </p>

    <p rev="IMPALA-1683">
      The following examples demonstrates the above rules.
    </p>

<codeblock rev="IMPALA-1683"><![CDATA[
-- Partition doesn't exist.
refresh p2 partition (y=0, z=3);
refresh p2 partition (y=0, z=-1)

-- Key columns specified in a different order than the table definition.
refresh p2 partition (z=1, y=0)

-- Incomplete partition spec causes an error.
refresh p2 partition (y=0)
ERROR: AnalysisException: Items in partition spec must exactly match the partition columns in the table definition: default.p2 (1 vs 2)
]]>
</codeblock>

    <p>
      For examples of using <codeph>REFRESH</codeph> and <codeph>INVALIDATE METADATA</codeph>
      with a combination of Impala and Hive operations, see
      <xref href="impala_tutorial.xml#tutorial_impala_hive"/>.
    </p>

    <p>
      <b>Related impala-shell options:</b>
    </p>

    <p rev="1.1">
      Due to the expense of reloading the metadata for all tables, the
      <cmdname>impala-shell</cmdname> <codeph>-r</codeph> option is not recommended.
    </p>

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

    <p rev="IMPALA-1683">
      All HDFS and Sentry permissions and privilege requirements are the same whether you
      refresh the entire table or a single partition.
    </p>

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

    <p>
      The <codeph>REFRESH</codeph> statement checks HDFS permissions of the underlying data
      files and directories, caching this information so that a statement can be cancelled
      immediately if for example the <codeph>impala</codeph> user does not have permission to
      write to the data directory for the table. Impala reports any lack of write permissions as
      an <codeph>INFO</codeph> message in the log file.
    </p>

    <p>
      If you change HDFS permissions to make data readable or writeable by the Impala user,
      issue another <codeph>REFRESH</codeph> to make Impala aware of the change.
    </p>

    <p rev="kudu" conref="../shared/impala_common.xml#common/kudu_blurb"/>

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

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

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

    <p>
      <xref href="impala_hadoop.xml#intro_metastore"/>,
      <xref href="impala_invalidate_metadata.xml#invalidate_metadata"/>
    </p>

  </conbody>

</concept>