我有一个Rails应用程序，能够按状态代码过滤记录。我注意到，当我通过“CA”作为搜索词时，我几乎可以立即得到结果。例如，如果我通过“AZ”，那就需要一分钟多的时间。
我不知道为什么？
下面是来自psql的查询说明：
快一点：
EXPLAIN ANALYZE SELECT
accounts.id
FROM "accounts"
LEFT OUTER JOIN "addresses"
ON "addresses"."addressable_id" = "accounts"."id"
AND "addresses"."address_type" = 'mailing'
AND "addresses"."addressable_type" = 'Account'
WHERE "accounts"."organization_id" = 16
AND (addresses.state_code IN ('CA'))
ORDER BY accounts.name DESC;
QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------------------------------
Sort (cost=4941.94..4941.94 rows=1 width=18) (actual time=74.810..74.969 rows=821 loops=1)
Sort Key: accounts.name
Sort Method: quicksort Memory: 75kB
-> Hash Join (cost=4.46..4941.93 rows=1 width=18) (actual time=70.044..73.148 rows=821 loops=1)
Hash Cond: (addresses.addressable_id = accounts.id)
-> Seq Scan on addresses (cost=0.00..4911.93 rows=6806 width=4) (actual time=0.027..65.547 rows=15244 loops=1)
Filter: (((address_type)::text = 'mailing'::text) AND ((addressable_type)::text = 'Account'::text) AND ((state_code)::text = 'CA'::text))
Rows Removed by Filter: 129688
-> Hash (cost=4.45..4.45 rows=1 width=18) (actual time=2.037..2.037 rows=1775 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 87kB
-> Index Scan using organization_id_index on accounts (cost=0.29..4.45 rows=1 width=18) (actual time=0.018..1.318 rows=1775 loops=1)
Index Cond: (organization_id = 16)
Planning time: 0.565 ms
Execution time: 75.224 ms
(14 rows)
慢一点：
EXPLAIN ANALYZE SELECT
accounts.id
FROM "accounts"
LEFT OUTER JOIN "addresses"
ON "addresses"."addressable_id" = "accounts"."id"
AND "addresses"."address_type" = 'mailing'
AND "addresses"."addressable_type" = 'Account'
WHERE "accounts"."organization_id" = 16
AND (addresses.state_code IN ('NV'))
ORDER BY accounts.name DESC;
QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------------------------------
Sort (cost=4917.27..4917.27 rows=1 width=18) (actual time=97091.270..97091.277 rows=25 loops=1)
Sort Key: accounts.name
Sort Method: quicksort Memory: 26kB
-> Nested Loop (cost=0.29..4917.26 rows=1 width=18) (actual time=844.250..97091.083 rows=25 loops=1)
Join Filter: (accounts.id = addresses.addressable_id)
Rows Removed by Join Filter: 915875
-> Index Scan using organization_id_index on accounts (cost=0.29..4.45 rows=1 width=18) (actual time=0.017..10.315 rows=1775 loops=1)
Index Cond: (organization_id = 16)
-> Seq Scan on addresses (cost=0.00..4911.93 rows=70 width=4) (actual time=0.110..54.521 rows=516 loops=1775)
Filter: (((address_type)::text = 'mailing'::text) AND ((addressable_type)::text = 'Account'::text) AND ((state_code)::text = 'NV'::text))
Rows Removed by Filter: 144416
Planning time: 0.308 ms
Execution time: 97091.325 ms
(13 rows)
慢一个结果是25行，快一个是821行，这更令人困惑。
最佳答案
我使用psql命令行中的VACUUM ANALYZE命令解决了这个问题。