argument of type <type>internal</type> and to return the pseudo-type

<type>table_am_handler</type>. The argument is a dummy value that simply

serves to prevent handler functions from being called directly from SQL commands.

</para>

<para>

Here is how an extension SQL script file might create a table access

method handler:

</para>

<programlisting>

CREATE OR REPLACE FUNCTION my_tableam_handler(internal)

RETURNS table_am_handler AS 'my_extension', 'my_tableam_handler'

LANGUAGE C STRICT;

CREATE ACCESS METHOD myam TYPE TABLE HANDLER my_tableam_handler;

</programlisting>

<para>

The result of the function must be a pointer to a struct of type

<structname>TableAmRoutine</structname>, which contains everything that the

core code needs to know to make use of the table access method. The return

value needs to be of server lifetime, which is typically achieved by

defining it as a <literal>static const</literal> variable in global

scope. The <structname>TableAmRoutine</structname> struct, also called the

defining it as a <literal>static const</literal> variable in global scope.

</para>

<para>

Here is how a source file with the table access method handler might

look like:

</para>

<programlisting><![CDATA[

#include "postgres.h"

#include "access/tableam.h"

#include "fmgr.h"

PG_MODULE_MAGIC;

static const TableAmRoutine my_tableam_methods = {

.type = T_TableAmRoutine,

/* Methods of TableAmRoutine omitted from example, add them here. */

};

PG_FUNCTION_INFO_V1(my_tableam_handler);

Datum

my_tableam_handler(PG_FUNCTION_ARGS)

{

PG_RETURN_POINTER(&my_tableam_methods);

}

]]>

</programlisting>

<para>

The <structname>TableAmRoutine</structname> struct, also called the

access method's <firstterm>API struct</firstterm>, defines the behavior of

the access method using callbacks. These callbacks are pointers to plain C

functions and are not visible or callable at the SQL level. All the