---
id: 'rum'
title: 'RUM: improved inverted index for full-text search based on GIN index'
description: 'A GIN-like index with additional tree-organized data for each index entry'
---

[RUM](https://github.com/postgrespro/rum) is an extension which adds a RUM index to Postgres.

RUM index is based on GIN that stores additional per-entry information in a posting tree. For example, positional information of lexemes or timestamps. In comparison to GIN it can use this information to make faster index-only scans for:

- Phrase search
- Text search with ranking by text distance operator
- Text `SELECT`s with ordering by some non-indexed additional column e.g. by timestamp.

RUM works best in scenarios when the possible keys are highly repeatable. I.e. all texts are composed of a
limited amount of words, so per-lexeme indexing gives significant speed-up in searching texts containing word
combinations or phrases.

Main operators for ordering are:

`tsvector` `<=>` `tsquery` | `float4` | Distance between `tsvector` and `tsquery`.
value `<=>` value | `float8` | Distance between two values.

Where value is `timestamp`, `timestamptz`, `int2`, `int4`, `int8`, `float4`, `float8`, `money` and `oid`

## Usage

### Enable the extension

You can get started with rum by enabling the extension in your Supabase dashboard.

<Tabs
  scrollable
  size="small"
  type="underlined"
  defaultActiveId="dashboard"
  queryGroup="database-method"
>
<TabPanel id="dashboard" label="Dashboard">

1. Go to the [Database](/dashboard/project/_/database/tables) page in the Dashboard.
2. Click on **Extensions** in the sidebar.
3. Search for "rum" and enable the extension.

</TabPanel>
<TabPanel id="sql" label="SQL">

```sql
-- Example: enable the "rum" extension
create extension rum with schema extensions;

-- Example: disable the "rum" extension
drop extension if exists rum;
```

</TabPanel>
</Tabs>

### Syntax

#### For type: `tsvector`

To understand the following you may need first to see [Official Postgres documentation on text
search](https://www.postgresql.org/docs/current/functions-textsearch.html)

`rum_tsvector_ops`

```sql
CREATE TABLE test_rum(t text, a tsvector);

CREATE TRIGGER tsvectorupdate
BEFORE UPDATE OR INSERT ON test_rum
FOR EACH ROW EXECUTE PROCEDURE tsvector_update_trigger('a', 'pg_catalog.english', 't');

INSERT INTO test_rum(t) VALUES ('The situation is most beautiful');
INSERT INTO test_rum(t) VALUES ('It is a beautiful');
INSERT INTO test_rum(t) VALUES ('It looks like a beautiful place');

CREATE INDEX rumidx ON test_rum USING rum (a rum_tsvector_ops);
```

And we can execute `tsvector` selects with ordering by text distance operator:

```sql
SELECT t, a `<=>` to_tsquery('english', 'beautiful | place') AS rank
    FROM test_rum
    WHERE a @@ to_tsquery('english', 'beautiful | place')
    ORDER BY a `<=>` to_tsquery('english', 'beautiful | place');
                t                |  rank
---------------------------------+---------
 It looks like a beautiful place | 8.22467
 The situation is most beautiful | 16.4493
 It is a beautiful               | 16.4493
(3 rows)
```

`rum_tsvector_addon_ops`

```sql
CREATE TABLE tsts (id int, t tsvector, d timestamp);
CREATE INDEX tsts_idx ON tsts USING rum (t rum_tsvector_addon_ops, d)
    WITH (attach = 'd', to = 't');
```

Now we can execute the selects with ordering distance operator on attached column:

```sql
SELECT id, d, d `<=>` '2016-05-16 14:21:25' FROM tsts WHERE t @@ 'wr&qh' ORDER BY d `<=>` '2016-05-16 14:21:25' LIMIT 5;
 id  |                d                |   ?column?
-----+---------------------------------+---------------
 355 | Mon May 16 14:21:22.326724 2016 |      2.673276
 354 | Mon May 16 13:21:22.326724 2016 |   3602.673276
 371 | Tue May 17 06:21:22.326724 2016 |  57597.326724
 406 | Wed May 18 17:21:22.326724 2016 | 183597.326724
 415 | Thu May 19 02:21:22.326724 2016 | 215997.326724
(5 rows)
```

#### For type: `anyarray`

`rum_anyarray_ops`

This operator class stores `anyarray` elements with length of the array. It supports operators `&&`, `@>`, `<@`, `=`, `%` operators. It also supports ordering by `<=>` operator.

```sql
CREATE TABLE test_array (i int2[]);
INSERT INTO test_array VALUES ('{}'), ('{0}'), ('{1,2,3,4}'), ('{1,2,3}'), ('{1,2}'), ('{1}');
CREATE INDEX idx_array ON test_array USING rum (i rum_anyarray_ops);
```

Now we can execute the query using index scan:

```sql
SELECT * FROM test_array WHERE i && '{1}' ORDER BY i `<=>` '{1}' ASC;
     i
-----------
 {1}
 {1,2}
 {1,2,3}
 {1,2,3,4}
(4 rows)
```

`rum_anyarray_addon_ops`

The does the same with `anyarray` index as `rum_tsvector_addon_ops` i.e. allows to order select results using distance
operator by attached column.

## Limitations

`RUM` has slower build and insert times than `GIN` due to:

1. It is bigger due to the additional attributes stored in the index.
2. It uses generic WAL records.

## Resources

- [Official RUM documentation](https://github.com/postgrespro/rum)