CREATE TABLE personal_data
(
    id 		     SERIAL    PRIMARY KEY
    , name 	     TEXT  	   NOT NULL
    , surname    TEXT      NOT NULL
    , patronymic TEXT      NULL
    , inn 	     TEXT      NULL
);

CREATE FUNCTION get_subject_key(name TEXT, surname TEXT, patronymic TEXT)
    RETURNS TEXT
    LANGUAGE SQL
    IMMUTABLE
    RETURN concat(name, surname, patronymic)
;

CREATE INDEX
    subject_fuzzy_search_idx
ON
    personal_data
USING
    GIST (
        get_subject_key(name, surname, patronymic)
        gist_trgm_ops
    )
;

EXPLAIN ANALYSE
SELECT 
	name,
	surname,
	get_subject_key(name, surname, patronymic) <-> get_subject_key('linu', 'storvalds', 'benedct') as dist
FROM
	personal_data
ORDER BY dist LIMIT 3;

Limit  (cost=0.41..1.61 rows=3 width=33) (actual time=6914.946..6915.083 rows=3 loops=1)
  ->  Index Scan using subject_fuzzy_search_idx on personal_data  (cost=0.41..795520.95 rows=2000002 width=33) (actual time=6914.945..6915.081 rows=3 loops=1)
"        Order By: (get_subject_key(name, surname, patronymic) <-> 'linustorvaldsbenedct'::text)"
Planning Time: 0.215 ms
Execution Time: 6936.034 ms