In addition to what Justin Cave wrote, since PostgreSQL 9.1 you can speed up any search with
~~*), and basic regular expression matches, too (
~). Use the operator classes provided by the module pg_trgm with a GIN or GiST index to speed up
LIKE expressions that are not left-anchored. To install the extension, run once per database:
CREATE EXTENSION IF NOT EXISTS pg_trgm;
Create an index of the form:
CREATE INDEX tbl_col_gin_trgm_idx ON tbl USING gin (col gin_trgm_ops);
CREATE INDEX tbl_col_gist_trgm_idx ON tbl USING gist (col gist_trgm_ops);
Creating and maintaining a GIN or GiST index carries a cost, but if your table is not heavily written, this is a great feature for you.
Depesz has an excellent article in his blog about the feature.
GIN or GiST?
These two quotes from the manual should provide some guidance
The choice between GiST and GIN indexing depends on the relative
performance characteristics of GiST and GIN, which are discussed
But for "nearest neighbour" type of queries with the using the distance operator
This can be implemented quite efficiently by GiST indexes, but not by