Postgres-XC 1.1 Documentation
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# F.5. btree_gist

> Note: The following description applies both to Postgres-XC and PostgreSQL if not described explicitly.

`btree_gist` provides GiST index operator classes that implement B-tree equivalent behavior for the data types `int2`, `int4`, `int8`, `float4`, `float8`, `numeric`, `timestamp with time zone`, `timestamp without time zone`, `time with time zone`, `time without time zone`, `date`, `interval`, `oid`, `money`, `char`, `varchar`, `text`, `bytea`, `bit`, `varbit`, `macaddr`, `inet`, and `cidr`.

In general, these operator classes will not outperform the equivalent standard B-tree index methods, and they lack one major feature of the standard B-tree code: the ability to enforce uniqueness. However, they provide some other features that are not available with a B-tree index, as described below. Also, these operator classes are useful when a multicolumn GiST index is needed, wherein some of the columns are of data types that are only indexable with GiST but other columns are just simple data types. Lastly, these operator classes are useful for GiST testing and as a base for developing other GiST operator classes.

In addition to the typical B-tree search operators, `btree_gist` also provides index support for `<>` ("not equals").

Also, for data types for which there is a natural distance metric, `btree_gist` defines a distance operator `<->`, and provides GiST index support for nearest-neighbor searches using this operator. Distance operators are provided for `int2`, `int4`, `int8`, `float4`, `float8`, `timestamp with time zone`, `timestamp without time zone`, `time without time zone`, `date`, `interval`, `oid`, and `money`.

## F.5.1. Example Usage

> Note: The following description applies both to Postgres-XC and PostgreSQL if not described explicitly.

Simple example using `btree_gist` instead of `btree`:

    CREATE TABLE test (a int4);
    -- create index
    CREATE INDEX testidx ON test USING gist (a);
    -- query
    SELECT * FROM test WHERE a < 10;
    -- nearest-neighbor search: find the ten entries closest to "42"
    SELECT *, a <-> 42 AS dist FROM test ORDER BY a <-> 42 LIMIT 10;

## F.5.2. Authors

Teodor Sigaev (`<teodor@stack.net>`) , Oleg Bartunov (`<oleg@sai.msu.su>`), and Janko Richter (`<jankorichter@yahoo.de>`). See http://www.sai.msu.su/~megera/postgres/gist/ for additional information.

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