operations (result) VALUES ('[quote $result]')"
$$ LANGUAGE pltcl;
</programlisting>
     Note that use of <function>catch</function> is still required for this
     purpose.  Otherwise the error would propagate to the top level of the
     function, preventing the desired insertion into
     the <structname>operations</structname> table.
     The <function>subtransaction</function> command does not trap errors, it
     only assures that all database operations executed inside its scope will
     be rolled back together when an error is reported.
    </para>

    <para>
     A rollback of an explicit subtransaction occurs on any error reported
     by the contained Tcl code, not only errors originating from database
     access.  Thus a regular Tcl exception raised inside
     a <function>subtransaction</function> command will also cause the
     subtransaction to be rolled back.  However, non-error exits out of the
     contained Tcl code (for instance, due to <function>return</function>) do
     not cause a rollback.
    </para>
   </sect1>

   <sect1 id="pltcl-transactions">
    <title>Transaction Management</title>

    <para>
     In a procedure called from the top level or an anonymous code block
     (<command>DO</command> command) called from the top level it is possible
     to control transactions.  To commit the current transaction, call the
     <literal>commit</literal> command.  To roll back the current transaction,
     call the <literal>rollback</literal> command.  (Note that it is not
     possible to run the SQL commands <command>COMMIT</command> or
     <command>ROLLBACK</command> via <function>spi_exec</function> or similar.
     It has to be done using these functions.)  After a transaction is ended,
     a new transaction is automatically started, so there is no separate
     command for that.
    </para>

    <para>
     Here is an example:
<programlisting>
CREATE PROCEDURE transaction_test1()
LANGUAGE pltcl
AS $$
for {set i 0} {$i &lt; 10} {incr i} {
    spi_exec "INSERT INTO test1 (a) VALUES ($i)"
    if {$i % 2 == 0} {
        commit
    } else {
        rollback
    }
}
$$;

CALL transaction_test1();
</programlisting>
    </para>

    <para>
     Transactions cannot be ended when an explicit subtransaction is active.
    </para>
   </sect1>

   <sect1 id="pltcl-config">
    <title>PL/Tcl Configuration</title>

    <para>
     This section lists configuration parameters that
     affect <application>PL/Tcl</application>.
    </para>

    <variablelist>

     <varlistentry id="guc-pltcl-start-proc" xreflabel="pltcl.start_proc">
      <term>
       <varname>pltcl.start_proc</varname> (<type>string</type>)
       <indexterm>
        <primary><varname>pltcl.start_proc</varname> configuration parameter</primary>
       </indexterm>
      </term>
      <listitem>
       <para>
        This parameter, if set to a nonempty string, specifies the name
        (possibly schema-qualified) of a parameterless PL/Tcl function that
        is to be executed whenever a new Tcl interpreter is created for
        PL/Tcl.  Such a function can perform per-session initialization, such
        as loading additional Tcl code.  A new Tcl interpreter is created