我的查询真的不那么复杂。它的运行时间接近250毫秒,这很慢。我使用EXPLAIN分析了查询并发现了seq扫描。我为此查询中使用的所有列都准备了适当的索引。所以我不确定从哪里开始。
这就是我所拥有的:
cl_production=# EXPLAIN SELECT count(DISTINCT events.id) AS count_distinct_events_id FROM "events" INNER JOIN "events_tickets" ON "events_tickets".event_id = "events".id INNER JOIN "tickets" ON "tickets".id = "events_tickets".ticket_id WHERE ((events.occurs_at > '2011-08-20 07:00:00.000000') AND (tickets.company_id = 175));
QUERY PLAN
------------------------------------------------------------------------------------------------------------------------
Aggregate (cost=15735.79..15735.80 rows=1 width=4)
-> Hash Join (cost=10540.01..15651.89 rows=33562 width=4)
Hash Cond: (events_tickets.event_id = events.id)
-> Hash Join (cost=3510.07..7516.61 rows=33562 width=4)
Hash Cond: (events_tickets.ticket_id = tickets.id)
-> Seq Scan on events_tickets (cost=0.00..1803.80 rows=124980 width=8)
-> Hash (cost=3058.63..3058.63 rows=27475 width=4)
-> Bitmap Heap Scan on tickets (cost=521.19..3058.63 rows=27475 width=4)
Recheck Cond: (company_id = 175)
-> Bitmap Index Scan on index_tickets_on_company_id (cost=0.00..514.33 rows=27475 width=0)
Index Cond: (company_id = 175)
-> Hash (cost=5963.87..5963.87 rows=64965 width=4)
-> Index Scan using index_events_on_occurs_at on events (cost=0.00..5963.87 rows=64965 width=4)
Index Cond: (occurs_at > '2011-08-20 07:00:00'::timestamp without time zone)
如上所述,以下是我的架构文件中的索引:
add_index "events_tickets", ["event_id", "ticket_id"], :name => "index_events_tickets_on_event_id_and_ticket_id", :unique => true
add_index "events_tickets", ["event_id"], :name => "index_events_tickets_on_event_id"
add_index "events_tickets", ["ticket_id"], :name => "index_events_tickets_on_ticket_id"
add_index "events", ["occurs_at"], :name => "index_events_on_occurs_at"
add_index "tickets", ["company_id"], :name => "index_tickets_on_company_id"
我假设序列扫描是什么杀死了这个查询。我在那张桌子上有很完整的索引。所以我迷路了。任何帮助将不胜感激。
感谢。
答案 0 :(得分:0)
您应该进行EXPLAIN ANALYZE以获取计划中每个节点的实际时间,而不仅仅是成本估算。
也许这种使用半连接而不是计数不同聚合的查询形式会有所帮助:
SELECT COUNT(*)
FROM events
WHERE EXISTS (SELECT 1
FROM events_tickets
JOIN tickets ON tickets.id = events_tickets.ticket_id
WHERE tickets.company_id = 175
AND events_tickets.event_id = events.id)
AND events.occurs_at > '2011-08-20 07:00:00'::timestamp