我试图确定是否有低成本＆＃34;以下查询的优化。我们已经实施了一个系统，其中包括“门票”和“门票”。赚取积分＆＃39;因此可以排名。为了支持分析类型的查询，我们存储每张票的等级，并将票与票一起捆绑。
我发现，在规模上，存储is_tied字段非常慢。我试图在一组＆＃34;门票＆＃34;上运行下面的场景。这是大约20-75k票。
我希望有人可以帮助确定原因并提供一些帮助。
我们在postgres 9.3.6
这是一个简化的票证表架构：
ogs_1=> \d api_ticket
Table "public.api_ticket"
Column | Type | Modifiers
------------------------------+--------------------------+---------------------------------------------------------
id | integer | not null default nextval('api_ticket_id_seq'::regclass)
status | character varying(3) | not null
points_earned | integer | not null
rank | integer | not null
event_id | integer | not null
user_id | integer | not null
is_tied | boolean | not null
Indexes:
"api_ticket_pkey" PRIMARY KEY, btree (id)
"api_ticket_4437cfac" btree (event_id)
"api_ticket_e8701ad4" btree (user_id)
"api_ticket_points_earned_idx" btree (points_earned)
"api_ticket_rank_idx" btree ("rank")
Foreign-key constraints:
"api_ticket_event_id_598c97289edc0e3e_fk_api_event_id" FOREIGN KEY (event_id) REFERENCES api_event(id) DEFERRABLE INITIALLY DEFERRED
(user_id) REFERENCES auth_user(id) DEFERRABLE INITIALLY DEFERRED
这是我正在执行的查询：
UPDATE api_ticket t SET is_tied = False
WHERE t.event_id IN (SELECT id FROM api_event WHERE status = 'c');
UPDATE api_ticket t SET is_tied = True
FROM (
SELECT event_id, rank
FROM api_ticket tt
WHERE event_id in (SELECT id FROM api_event WHERE status = 'c')
AND tt.status <> 'x'
GROUP BY rank, event_id
HAVING count(*) > 1
) AS tied_tickets
WHERE t.rank = tied_tickets.rank AND
tied_tickets.event_id = t.event_id;
这里有一组约35,000行的解释：
QUERY PLAN
----------------------------------------------------------------------------------------------------------------------------
Update on api_ticket t (cost=3590.01..603570.21 rows=157 width=128)
-> Nested Loop (cost=3590.01..603570.21 rows=157 width=128)
-> Subquery Scan on tied_tickets (cost=2543.31..2556.18 rows=572 width=40)
-> HashAggregate (cost=2543.31..2550.46 rows=572 width=8)
Filter: (count(*) > 1)
-> Nested Loop (cost=0.84..2539.02 rows=572 width=8)
-> Index Scan using api_event_status_idx1 on api_event (cost=0.29..8.31 rows=1 width=4)
Index Cond: ((status)::text = 'c'::text)
-> Index Scan using api_ticket_4437cfac on api_ticket tt (cost=0.55..2524.99 rows=572 width=8)
Index Cond: (event_id = api_event.id)
Filter: ((status)::text <> 'x'::text)
-> Bitmap Heap Scan on api_ticket t (cost=1046.70..1050.71 rows=1 width=92)
Recheck Cond: (("rank" = tied_tickets."rank") AND (event_id = tied_tickets.event_id))
-> BitmapAnd (cost=1046.70..1046.70 rows=1 width=0)
-> Bitmap Index Scan on api_ticket_rank_idx (cost=0.00..26.65 rows=708 width=0)
Index Cond: ("rank" = tied_tickets."rank")
-> Bitmap Index Scan on api_ticket_4437cfac (cost=0.00..1019.79 rows=573 width=0)
Index Cond: (event_id = tied_tickets.event_id)