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e4309f73f6
This enables sortsupport in the btree_gist extension for faster builds
of gist indexes.
Sorted gist index build strategy is the new default now. Regression
tests are unchanged (except for one small change in the 'enum' test to
add coverage for enum values added later) and are using the sorted
build strategy instead.
One version of this was committed a long time ago already, in commit
9f984ba6d2, but it was quickly reverted because of buildfarm
failures. The failures were presumably caused by some small bugs, but
we never got around to debug and commit it again. This patch was
written from scratch, implementing the same idea, with some fragments
and ideas from the original patch.
Author: Bernd Helmle <mailings@oopsware.de>
Author: Andrey Borodin <x4mmm@yandex-team.ru>
Discussion: https://www.postgresql.org/message-id/64d324ce2a6d535d3f0f3baeeea7b25beff82ce4.camel@oopsware.de
126 lines
4.8 KiB
Plaintext
126 lines
4.8 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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By default <filename>btree_gist</filename> builds <acronym>GiST</acronym> index with
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<function>sortsupport</function> in <firstterm>sorted</firstterm> mode. This usually results in
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much faster index built speed. It is still possible to revert to buffered built strategy
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by using the <literal>buffering</literal> parameter when creating the index.
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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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