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The original titles only had the module name, which is not very useful when scanning the list. By adding a very brief description to each title, the table of contents becomes friendlier. Also amend the introduction in the "additional modules" appendix, using the word "Extension" more extensively. Nowadays, almost all contrib modules are extensions, so this is also helpful. Author: Karl O. Pinc <kop@karlpinc.com> Reviewed-by: Brar Piening <brar@gmx.de> Discussion: https://postgr.es/m/20230102180015.372995a9@slate.karlpinc.com
119 lines
4.4 KiB
Plaintext
119 lines
4.4 KiB
Plaintext
<!-- doc/src/sgml/btree-gist.sgml -->
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<sect1 id="btree-gist" xreflabel="btree_gist">
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<title>btree_gist — GiST operator classes with B-tree behavior</title>
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<indexterm zone="btree-gist">
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<primary>btree_gist</primary>
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</indexterm>
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<para>
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<filename>btree_gist</filename> provides GiST index operator classes that
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implement B-tree equivalent behavior for the data types
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<type>int2</type>, <type>int4</type>, <type>int8</type>, <type>float4</type>,
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<type>float8</type>, <type>numeric</type>, <type>timestamp with time zone</type>,
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<type>timestamp without time zone</type>, <type>time with time zone</type>,
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<type>time without time zone</type>, <type>date</type>, <type>interval</type>,
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<type>oid</type>, <type>money</type>, <type>char</type>,
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<type>varchar</type>, <type>text</type>, <type>bytea</type>, <type>bit</type>,
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<type>varbit</type>, <type>macaddr</type>, <type>macaddr8</type>, <type>inet</type>,
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<type>cidr</type>, <type>uuid</type>, <type>bool</type> and all <type>enum</type> types.
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</para>
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<para>
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In general, these operator classes will not outperform the equivalent
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standard B-tree index methods, and they lack one major feature of the
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standard B-tree code: the ability to enforce uniqueness. However,
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they provide some other features that are not available with a B-tree
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index, as described below. Also, these operator classes are useful
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when a multicolumn GiST index is needed, wherein some of the columns
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are of data types that are only indexable with GiST but other columns
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are just simple data types. Lastly, these operator classes are useful for
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GiST testing and as a base for developing other GiST operator classes.
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</para>
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<para>
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In addition to the typical B-tree search operators, <filename>btree_gist</filename>
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also provides index support for <literal><></literal> (<quote>not
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equals</quote>). This may be useful in combination with an
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<link linkend="sql-createtable-exclude">exclusion constraint</link>,
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as described below.
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</para>
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<para>
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Also, for data types for which there is a natural distance metric,
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<filename>btree_gist</filename> defines a distance operator <literal><-></literal>,
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and provides GiST index support for nearest-neighbor searches using
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this operator. Distance operators are provided for
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<type>int2</type>, <type>int4</type>, <type>int8</type>, <type>float4</type>,
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<type>float8</type>, <type>timestamp with time zone</type>,
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<type>timestamp without time zone</type>,
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<type>time without time zone</type>, <type>date</type>, <type>interval</type>,
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<type>oid</type>, and <type>money</type>.
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</para>
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<para>
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This module is considered <quote>trusted</quote>, that is, it can be
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installed by non-superusers who have <literal>CREATE</literal> privilege
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on the current database.
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</para>
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<sect2 id="btree-gist-example-usage">
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<title>Example Usage</title>
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<para>
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Simple example using <literal>btree_gist</literal> instead of <literal>btree</literal>:
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</para>
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<programlisting>
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CREATE TABLE test (a int4);
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-- create index
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CREATE INDEX testidx ON test USING GIST (a);
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-- query
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SELECT * FROM test WHERE a < 10;
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-- nearest-neighbor search: find the ten entries closest to "42"
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SELECT *, a <-> 42 AS dist FROM test ORDER BY a <-> 42 LIMIT 10;
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</programlisting>
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<para>
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Use an <link linkend="sql-createtable-exclude">exclusion
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constraint</link> to enforce the rule that a cage at a zoo
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can contain only one kind of animal:
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</para>
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<programlisting>
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=> CREATE TABLE zoo (
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cage INTEGER,
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animal TEXT,
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EXCLUDE USING GIST (cage WITH =, animal WITH <>)
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);
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=> INSERT INTO zoo VALUES(123, 'zebra');
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INSERT 0 1
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=> INSERT INTO zoo VALUES(123, 'zebra');
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INSERT 0 1
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=> INSERT INTO zoo VALUES(123, 'lion');
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ERROR: conflicting key value violates exclusion constraint "zoo_cage_animal_excl"
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DETAIL: Key (cage, animal)=(123, lion) conflicts with existing key (cage, animal)=(123, zebra).
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=> INSERT INTO zoo VALUES(124, 'lion');
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INSERT 0 1
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</programlisting>
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</sect2>
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<sect2 id="btree-gist-authors">
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<title>Authors</title>
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<para>
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Teodor Sigaev (<email>teodor@stack.net</email>),
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Oleg Bartunov (<email>oleg@sai.msu.su</email>),
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Janko Richter (<email>jankorichter@yahoo.de</email>), and
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Paul Jungwirth (<email>pj@illuminatedcomputing.com</email>). See
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<ulink url="http://www.sai.msu.su/~megera/postgres/gist/"></ulink>
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for additional information.
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</para>
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</sect2>
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</sect1>
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