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<refentry id="SQL-START-TRANSACTION">

<docinfo>

<date>2002-07-26</date>

</docinfo>

<refmeta>

<refentrytitle id="SQL-START-TRANSACTION-TITLE">START TRANSACTION</refentrytitle>

<refmiscinfo>SQL - Language Statements</refmiscinfo>

</refmeta>

<refnamediv>

<refname>START TRANSACTION</refname>

<refpurpose>start a transaction block</refpurpose>

</refnamediv>

<refsynopsisdiv>

<synopsis>

START TRANSACTION [ ISOLATION LEVEL { READ COMMITTED | SERIALIZABLE } ]

</synopsis>

<refsect2 id="R2-SQL-START-TRANSACTION-1">

<refsect2info>

<date>1998-09-27</date>

</refsect2info>

<title>

Inputs

</title>

<para>

None.

</para>

</refsect2>

<refsect2 id="R2-SQL-START-TRANSACTION-2">

<refsect2info>

<date>1998-09-27</date>

</refsect2info>

<title>

Outputs

</title>

<para>

<variablelist>

<varlistentry>

<term><computeroutput>

START TRANSACTION

</computeroutput></term>

<listitem>

<para>

Message returned if successful.

</para>

</listitem>

</varlistentry>

<varlistentry>

<term><computeroutput>

WARNING: BEGIN: already a transaction in progress

</computeroutput></term>

<listitem>

<para>

If there is already a transaction in progress when the

command is issued.

</para>

</listitem>

</varlistentry>

</variablelist>

</para>

</refsect2>

</refsynopsisdiv>

<refsect1>

<title>Description</title>

<para>

This command begins a new transaction. If the isolation level is

specified, the new transaction has that isolation level. In all other

respects, the behavior of this command is identical to the

<command>BEGIN</command>.

</para>

</refsect1>

<refsect1>

<title>Notes</title>

<para>

The isolation level of a transaction can also be set with the <xref

linkend="sql-set-transaction" endterm="sql-set-transaction-title">.

If no isolation level is specified, the level defaults to

<option>READ COMMITTED</option>.

</para>

</refsect1>

<refsect1 id="R1-SQL-START-TRANSACTION-3">

<title>Compatibility</title>

<refsect2 id="R2-SQL-START-TRANSACTION-4">

<title>SQL99</title>

<para>

<option>SERIALIZABLE</option> is the default level in

<acronym>SQL</acronym>. <productname>PostgreSQL</productname>

does not provide the isolation levels <option>READ UNCOMMITTED</option>

and <option>REPEATABLE READ</option>. Because of multiversion

concurrency control, the <option>SERIALIZABLE</option> level is

not truly serializable. See the <citetitle>User's Guide</citetitle>

for details.

</para>

<para>

In <acronym>SQL99</acronym> this statement can specify two other

properties of the new transaction: whether the transaction is

read-only and the size of the diagnostics area. Neither of these

concepts are currently supported in

<productname>PostgreSQL</productname>.

</para>

</refsect2>

</refsect1>

</refentry>

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