specified by the index method.

</para>

<para>

Additionally, some opclasses allow users to specify parameters which

control their behavior. Each builtin index access method has an optional

<function>options</function> support function, which defines a set of

opclass-specific parameters.

</para>

<para>

B-trees require a comparison support function,

and allowthree additional support functions to be

and allowfour additional support functions to be

supplied at the operator class author's option, as shown in <xref

linkend="xindex-btree-support-table"/>.

The requirements for these support functions are explained further in

<xref linkend="btree-support-funcs"/>.

</para>

<para>

Additionally, some opclasses allow users to specify parameters which

control their behavior. Each builtin index access method has an optional

<function>options</function> support function, which defines a set of

opclass-specific parameters.

</para>

<table tocentry="1" id="xindex-btree-support-table">

<title>B-Tree Support Functions</title>

<tgroup cols="2">

</table>

<para>

Hash indexes require one support function, and allowa second one to be

supplied at the operator class author's option, as shown in <xref

Hash indexes require one support function, and allowtwo additional ones to

besupplied at the operator class author's option, as shown in <xref

linkend="xindex-hash-support-table"/>.

</para>

</table>

<para>

GiST indexes havenine support functions,two of which are optional,

GiST indexes haveten support functions,three of which are optional,

as shown in <xref linkend="xindex-gist-support-table"/>.

(For more information see <xref linkend="gist"/>.)

</para>

</table>

<para>

SP-GiST indexesrequire five support functions, as

SP-GiST indexeshave six support functions, one of which is optional, as

shown in <xref linkend="xindex-spgist-support-table"/>.

(For more information see <xref linkend="spgist"/>.)

</para>

</table>

<para>

GIN indexes havesix support functions,three of which are optional,

GIN indexes haveseven support functions,four of which are optional,

as shown in <xref linkend="xindex-gin-support-table"/>.

(For more information see <xref linkend="gin"/>.)

</para>

</table>

<para>

BRIN indexes havefour basic support functions,as shown in

<xref linkend="xindex-brin-support-table"/>; those basic functions

may require additional support functions to be provided.

BRIN indexes havefive basic support functions,one of which is optional,

as shown in<xref linkend="xindex-brin-support-table"/>. Some versions of

the basic functions require additional support functions to be provided.

(For more information see <xref linkend="brin-extensibility"/>.)

</para>