Very slow query

The following query on some small datasets takes over a second to run.
I'd be grateful for some help in understanding the explain output, and
to remake the code.

Looks like the sort is using up quite a bit of resources. I made an
index on boards using columns "b.n_type, b.n_id, b.t_name" but the index
was not recorded in explain analyze. (see "testindex" below).

I am using PostgreSQL 7.4.2 on i386-pc-linux-gnu (Debian). The query is
in a psql function (I've changed variables to hard coded integers
below). The db is vacuumed every night.

Thanks for any help;
Rory

SELECT DISTINCT
b.n_id as id,
b.n_type,
CASE b.n_type WHEN 0 THEN 'personal'
WHEN 1 THEN 'private'
WHEN 2 THEN 'blog'
ELSE 'public'
END as type,
b.t_name as title
FROM
boards b, people p, objects o
WHERE
b.b_hidden = 'f'
AND
(
b.n_type = 3
OR
b.n_creator = 71
OR
( b.n_id = o.n_board_id
AND
o.n_creator = 71
AND
o.n_joined > 0
)
)
ORDER BY
b.n_type, b.n_id ASC, b.t_name;

trial=> \d boards
Table "public.boards"
Column | Type | Modifiers
---------------+-----------------------------+----------------------------------------------------------
n_id | integer | not null default nextval('public.boards_n_id_seq'::text)
b_hidden | boolean | default false
dt_created | timestamp without time zone | default ('now'::text)::timestamp(6) with time zone
dt_modified | timestamp without time zone | default ('now'::text)::timestamp(6) with time zone
t_mobile | character varying(15) |
t_email | character varying(50) |
n_creator | integer | not null
n_type | smallint | not null default 0
t_name | character varying(100) | not null
t_description | character varying(500) |
n_id_photo | integer |
n_bg_colour | integer | default 0
Indexes:
"boards_pkey" primary key, btree (n_id)
"boards_t_email_key" unique, btree (t_email)
"boards_t_mobile_key" unique, btree (t_mobile)
"testindex" btree (n_type, n_id, t_name)
Foreign-key constraints:
"$1" FOREIGN KEY (n_creator) REFERENCES people(n_id) ON UPDATE CASCADE ON DELETE CASCADE
"$2" FOREIGN KEY (n_id_photo) REFERENCES photo(n_id) ON UPDATE CASCADE ON DELETE SET NULL
Triggers:
tr_update_modified_time BEFORE UPDATE ON boards FOR EACH ROW EXECUTE PROCEDURE fn_update_modified_time()

trial=> \d people
Table "public.people"
Column | Type | Modifiers
-------------------+-----------------------------+----------------------------------------------------------
n_id | integer | not null default nextval('public.people_n_id_seq'::text)
n_object_id | integer |
n_objects_counter | integer | default 0
b_hidden | boolean | default false
dt_created | timestamp without time zone | default ('now'::text)::timestamp(6) with time zone
dt_modified | timestamp without time zone | default ('now'::text)::timestamp(6) with time zone
t_nickname | character varying(20) | not null
t_firstname | character varying(20) | not null
t_surname | character varying(25) | not null
t_mobile | character varying(15) |
t_email | character varying(50) |
t_password | character varying(15) | not null
b_registered | boolean | default false
n_email_status | smallint | default 0
n_txt_status | smallint | default 0
b_work_hours | boolean | default false
b_confirmations | boolean | default true
Indexes:
"people_pkey" primary key, btree (n_id)
"people_t_email_key" unique, btree (t_email)
"people_t_mobile_key" unique, btree (t_mobile)
"people_t_nickname_key" unique, btree (t_nickname)
Foreign-key constraints:
"object_chk" FOREIGN KEY (n_object_id) REFERENCES objects(n_id) ON UPDATE CASCADE ON DELETE SET NULL
Triggers:
tr_update_modified_time BEFORE UPDATE ON people FOR EACH ROW EXECUTE PROCEDURE fn_update_modified_time()

trial=> \d objects
Table "public.objects"
Column | Type | Modifiers
---------------+-----------------------------+-----------------------------------------------------------
n_id | integer | not null default nextval('public.objects_n_id_seq'::text)
t_text_id | character varying(25) | not null
b_hidden | boolean | default false
dt_created | timestamp without time zone | default ('now'::text)::timestamp(6) with time zone
dt_modified | timestamp without time zone | default ('now'::text)::timestamp(6) with time zone
n_creator | integer | not null
n_type | smallint | not null default 0
t_name | character varying(100) | not null
t_description | text |
t_postcode | character varying(10) |
n_id_photo | integer |
n_board_id | integer | not null
n_joined | smallint |
b_trigger | boolean | default true
Indexes:
"objects_pkey" primary key, btree (n_id)
Foreign-key constraints:
"$1" FOREIGN KEY (n_creator) REFERENCES people(n_id) ON UPDATE CASCADE ON DELETE CASCADE
"$2" FOREIGN KEY (n_id_photo) REFERENCES photo(n_id) ON UPDATE CASCADE ON DELETE SET NULL
"$3" FOREIGN KEY (n_board_id) REFERENCES boards(n_id) ON UPDATE CASCADE ON DELETE CASCADE

Unique (cost=3677.26..3711.48 rows=102 width=18) (actual time=12566.422..13045.404 rows=4 loops=1)
-> Sort (cost=3677.26..3684.10 rows=2738 width=18) (actual time=12566.413..12809.928 rows=158254 loops=1)
Sort Key: b.n_type, b.n_id, b.t_name, CASE WHEN (b.n_type = 0) THEN 'personal'::text WHEN (b.n_type = 1) THEN 'private'::te
xt WHEN (b.n_type = 2) THEN 'blog'::text ELSE 'public'::text END
-> Nested Loop (cost=3442.79..3520.93 rows=2738 width=18) (actual time=0.244..1052.180 rows=158254 loops=1)
-> Seq Scan on people p (cost=0.00..2.67 rows=67 width=0) (actual time=0.012..0.709 rows=67 loops=1)
-> Materialize (cost=3442.79..3443.20 rows=41 width=18) (actual time=0.005..6.528 rows=2362 loops=67)
-> Nested Loop (cost=3.27..3442.79 rows=41 width=18) (actual time=0.216..273.709 rows=2362 loops=1)
Join Filter: ((("inner".n_id = "outer".n_board_id) OR ("inner".n_type = 3) OR ("inner".n_creator = 71)) A
ND (("outer".n_creator = 71) OR ("inner".n_type = 3) OR ("inner".n_creator = 71)) AND (("outer".n_joined > 0) OR ("inner".n_type = 3
) OR ("inner".n_creator = 71)))
-> Seq Scan on objects o (cost=0.00..27.87 rows=787 width=10) (actual time=0.005..1.372 rows=787 loops=
1)
-> Materialize (cost=3.27..4.29 rows=102 width=22) (actual time=0.001..0.105 rows=102 loops=787)
-> Seq Scan on boards b (cost=0.00..3.27 rows=102 width=22) (actual time=0.017..0.352 rows=102 lo
ops=1)
Filter: (b_hidden = false)
Total runtime: 13051.065 ms

--
Rory Campbell-Lange
<rory(at)campbell-lange(dot)net>
<www.campbell-lange.net>