2002-08-06 07:32:16 +02:00
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<!-- $Header: /cvsroot/pgsql/doc/src/sgml/ref/start_transaction.sgml,v 1.2 2002/08/06 05:32:16 momjian Exp $ -->
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2002-08-04 07:14:06 +02:00
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<refentry id="SQL-START-TRANSACTION">
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<docinfo>
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<date>2002-07-26</date>
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</docinfo>
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<refmeta>
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<refentrytitle id="SQL-START-TRANSACTION-TITLE">START TRANSACTION</refentrytitle>
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<refmiscinfo>SQL - Language Statements</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>START TRANSACTION</refname>
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<refpurpose>start a transaction block</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<synopsis>
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START TRANSACTION [ ISOLATION LEVEL { READ COMMITTED | SERIALIZABLE } ]
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</synopsis>
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<refsect2 id="R2-SQL-START-TRANSACTION-1">
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<refsect2info>
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<date>1998-09-27</date>
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</refsect2info>
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<title>
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Inputs
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</title>
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<para>
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None.
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</para>
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</refsect2>
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<refsect2 id="R2-SQL-START-TRANSACTION-2">
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<refsect2info>
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<date>1998-09-27</date>
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</refsect2info>
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<title>
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Outputs
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</title>
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<para>
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<variablelist>
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<varlistentry>
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<term><computeroutput>
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START TRANSACTION
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</computeroutput></term>
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<listitem>
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<para>
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Message returned if successful.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><computeroutput>
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WARNING: BEGIN: already a transaction in progress
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</computeroutput></term>
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<listitem>
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<para>
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If there is already a transaction in progress when the
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command is issued.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsect2>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>
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This command begins a new transaction. If the isolation level is
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specified, the new transaction has that isolation level. In all other
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respects, the behavior of this command is identical to the
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2002-08-06 07:32:16 +02:00
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<command>BEGIN</command> command.
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</para>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para>
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The isolation level of a transaction can also be set with the <xref
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2002-08-06 07:32:16 +02:00
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linkend="sql-set-transaction" endterm="sql-set-transaction-title">
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command. If no isolation level is specified, the level defaults to
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<option>READ COMMITTED</option>.
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</para>
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</refsect1>
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<refsect1 id="R1-SQL-START-TRANSACTION-3">
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<title>Compatibility</title>
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<refsect2 id="R2-SQL-START-TRANSACTION-4">
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<title>SQL99</title>
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<para>
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<option>SERIALIZABLE</option> is the default level in
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<acronym>SQL</acronym>. <productname>PostgreSQL</productname>
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does not provide the isolation levels <option>READ UNCOMMITTED</option>
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and <option>REPEATABLE READ</option>. Because of multiversion
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concurrency control, the <option>SERIALIZABLE</option> level is
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not truly serializable. See the <citetitle>User's Guide</citetitle>
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for details.
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</para>
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<para>
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In <acronym>SQL99</acronym> this statement can specify two other
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properties of the new transaction: whether the transaction is
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read-only and the size of the diagnostics area. Neither of these
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concepts are currently supported in
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<productname>PostgreSQL</productname>.
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</para>
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</refsect2>
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</refsect1>
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</refentry>
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<!-- Keep this comment at the end of the file
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Local variables:
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End:
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-->
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