F.55. rum

F.55.1. Introduction

The rum module provides access method to work with the RUM indexes. It is based on the GIN access methods code.

GIN index allows to perform fast full-text search using tsvector and tsquery types. However, full-text search with GIN index has the following drawbacks:

  • Slow ranking. Ranking requires positional information, but GIN index does not store positions of lexemes. So after the index scan we need an additional heap scan to retrieve lexeme positions.

  • Slow phrase search. This problem is related to the previous one as phrase search also needs positional information.

  • Slow ordering by timestamp. GIN index cannot store any additional information together with lexemes, so it is necessary to perform a heap scan.

RUM solves these issues by storing additional information in posting tree. In particular, it stores positional information of lexemes or timestamps.

The drawback of RUM is that it has slower build and insert time as compared to GIN because RUM stores additional information together with keys and uses generic WAL records.

F.55.2. Installation

rum is a Postgres Pro Enterprise extension and it has no special prerequisites.

Install extension as follows:

$ psql dbname -c "CREATE EXTENSION rum"

F.55.3. Common Operators

The operators provided by the rum module are shown in Table F.40:

Table F.40. rum Operators

OperatorReturnsDescription
tsvector <=> tsqueryfloat4Returns distance between tsvector and tsquery values.
timestamp <=> timestampfloat8Returns distance between two timestamp values.
timestamp <=| timestampfloat8Returns distance only for ascending timestamp values.
timestamp |=> timestampfloat8Returns distance only for descending timestamp values.

F.55.4. Operator Classes

The rum extension provides the following operator classes:

rum_tsvector_ops

Stores tsvector lexemes with positional information. Supports ordering by <=> operator and prefix search.

rum_tsvector_hash_ops

Stores hash of tsvector lexemes with positional information. Supports ordering by <=> operator, but does not support prefix search.

rum_tsvector_addon_ops

Stores tsvector lexemes with additional data of any type supported by RUM.

rum_tsvector_hash_addon_ops

Stores tsvector lexemes with additional data of any type supported by RUM. Does not support prefix search.

rum_tsquery_ops

Stores branches of query tree in additional information.

rum_anyarray_ops

Stores anyarrray elements with length of the array. Supports ordering by <=> operator.

Indexable operators: && @> <@ = %

rum_anyarray_addon_ops

Stores anyarray elements with additional data of any type supported by RUM.

rum_type_ops

Stores lexemes of the corresponding type with positional information. The type placeholder in the class name must be substituted by one of the following type names: int2, int4, int8, float4, float8, money, oid, timestamp, timestamptz, time, timetz, date, interval, macaddr, inet, cidr, text, varchar, char, bytea, bit, varbit, numeric.

rum_type_ops supports ordering by <=>, <=|, and |=> operators. This operator class can be used together with rum_tsvector_addon_ops, rum_tsvector_hash_addon_ops, and rum_anyarray_addon_ops operator classes.

Supported indexable operators depend on the data type:

  • < <= = >= > <=> <=| |=> are supported for int2, int4, int8, float4, float8, money, oid, timestamp, timestamptz.

  • < <= = >= > are supported for time, timetz, date, interval, macaddr, inet, cidr, text, varchar, char, bytea, bit, varbit, numeric.

Note

The following operator classes are now deprecated: rum_tsvector_timestamp_ops, rum_tsvector_timestamptz_ops, rum_tsvector_hash_timestamp_ops, rum_tsvector_hash_timestamptz_ops.

F.55.5. Examples

F.55.5.1.  rum_tsvector_ops Example

Let's assume we have the following table:

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');

Then we can create a new index:

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

And we can execute the following queries:

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
---------------------------------+-----------
 The situation is most beautiful | 0.0303964
 It is a beautiful               | 0.0303964
 It looks like a beautiful place | 0.0607927
(3 rows)

SELECT t, a <=> to_tsquery('english', 'place | situation') AS rank
    FROM test_rum
    WHERE a @@ to_tsquery('english', 'place | situation')
    ORDER BY a <=> to_tsquery('english', 'place | situation');
                t                |   rank
---------------------------------+-----------
 The situation is most beautiful | 0.0303964
 It looks like a beautiful place | 0.0303964
(2 rows)

F.55.5.2.  rum_tsvector_addon_ops Example

Let's assume we have the following table:

CREATE TABLE tsts (id int, t tsvector, d timestamp);

\copy tsts from 'rum/data/tsts.data'

CREATE INDEX tsts_idx ON tsts USING rum (t rum_tsvector_addon_ops, d)
    WITH (attach = 'd', to = 't');

Now we can execute the following queries:

EXPLAIN (costs off)
    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;
                                    QUERY PLAN                                     
-----------------------------------------------------------------------------------
 Limit
   ->  Index Scan using tsts_idx on tsts
         Index Cond: (t @@ '''wr'' & ''qh'''::tsquery)
         Order By: (d <=> 'Mon May 16 14:21:25 2016'::timestamp without time zone)
(4 rows)

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)

F.55.5.3.  rum_tsquery_ops Example

Suppose we have the table:

CREATE TABLE query (q tsquery, tag text);

INSERT INTO query VALUES ('supernova & star', 'sn'),
    ('black', 'color'),
    ('big & bang & black & hole', 'bang'),
    ('spiral & galaxy', 'shape'),
    ('black & hole', 'color');

CREATE INDEX query_idx ON query USING rum(q);

We can execute the following fast query:

SELECT * FROM query
    WHERE to_tsvector('black holes never exists before we think about them') @@ q;
        q         |  tag  
------------------+-------
 'black'          | color
 'black' & 'hole' | color
(2 rows)

F.55.5.4.  rum_anyarray_ops Example

Let's assume we have the following table:

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 following query using index scan:

SET enable_seqscan TO off;

EXPLAIN (COSTS OFF) SELECT * FROM test_array WHERE i && '{1}' ORDER BY i <=> '{1}' ASC;
                QUERY PLAN
------------------------------------------
 Index Scan using idx_array on test_array
   Index Cond: (i && '{1}'::smallint[])
   Order By: (i <=> '{1}'::smallint[])
(3 rows)

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)

F.55.6. Authors

Alexander Korotkov Postgres Professional Ltd., Russia

Oleg Bartunov Postgres Professional Ltd., Russia

Teodor Sigaev Postgres Professional Ltd., Russia