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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="transactions">

  <title>Impala Transactions</title>

  <titlealts audience="PDF">

    <navtitle>Transactions</navtitle>

  </titlealts>

  <conbody>

    <p>
      A transaction is a single logical operation on the data. Impala supports transactions that
      satisfy a level of consistency that improves the integrity and reliability of the data
      before and after a transaction.
    </p>

    <p>
      Specifically, Impala provides atomicity and isolation of insert operations on
      transactional tables. A single table insert is either committed in full or not committed,
      and the results of the insert operation are not visible to other query operations until
      the operation is committed.
    </p>

    <p>
      For single table, the inserts are ordered, so if Impala doesn't see a committed insert, it
      won't see any insert committed after it.
    </p>

    <p>
      For insert-only transactional tables, you can perform the following statements:
      <codeph>CREATE TABLE</codeph>, <codeph>DROP TABLE</codeph>, <codeph>TRUNCATE</codeph>,
      <codeph>INSERT</codeph>, <codeph>SELECT</codeph>
    </p>

    <p>
      All transactions in Impala automatically commit at the end of the statement. Currently,
      Impala does not support multi-statement transactions.
    </p>

    <p>
      Insert-only tables must be the managed and file-format based tables, such as Parquet,
      Avro, and text.
    </p>

    <note>
      Impala does not support changing transactional properties of tables. For example, you
      cannot alter a transactional table to a non-transactional table.
    </note>

  </conbody>

</concept>