docs/topics/impala_kudu_read_mode.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--
Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements.  See the NOTICE file
distributed with this work for additional information
regarding copyright ownership.  The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License.  You may obtain a copy of the License at

  http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied.  See the License for the
specific language governing permissions and limitations
under the License.
-->
<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="kudu_read_mode" rev="3.1.0 IMPALA-6812">

  <title>KUDU_READ_MODE Query Option (<keyword keyref="impala31"/> or higher only)</title>

  <titlealts audience="PDF">

    <navtitle>KUDU_READ_MODE</navtitle>

  </titlealts>

  <prolog>
    <metadata>
      <data name="Category" value="Impala"/>
      <data name="Category" value="Impala Query Options"/>
      <data name="Category" value="Performance"/>
      <data name="Category" value="Developers"/>
      <data name="Category" value="Data Analysts"/>
    </metadata>
  </prolog>

  <conbody>

    <p rev="3.1.0 IMPALA-6812">
      The <codeph>KUDU_READ_MODE</codeph> query option allows you to set a desired consistency
      level for scans of Kudu tables.
    </p>

    <p>
      <b>Type:</b> String
    </p>

    <p>
      <b>Default:</b> <codeph>"DEFAULT"</codeph>
    </p>

    <p>
      <b>Added in:</b> <keyword keyref="impala31"/>
    </p>

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

    <p>
      The following values are supported for the query option:
      <ul>
        <li>
          <codeph>"DEFAULT"</codeph>: The value of the startup flag,
            <codeph>&#8209;&#8209;kudu_read_mode</codeph>, is used. </li>

        <li>
          <codeph>"READ_LATEST"</codeph>: Commonly known as the Read Committed isolation mode,
          in this mode, Kudu provides no consistency guarantees for this mode, except that all
          returned rows were committed at some point.
        </li>

        <li>
          <codeph>"READ_AT_SNAPSHOT"</codeph>: Kudu will take a snapshot of the current state of
          the data and perform the scan over the snapshot, possibly after briefly waiting for
          ongoing writes to complete. This provides "Read Your Writes" consistency within a
          single Impala session, except in the case of a Kudu leader change. See the Kudu
          documentation for more details.
        </li>
      </ul>
    </p>

  </conbody>

</concept>