Postgresql在索引列上查询非常慢
我有50万行的桌子。 一列名为u_sphinx是非常重要的可用值是1,2,3。 现在所有的行都有值3，但是，当我检查新行（u_sphinx = 1）时，查询非常缓慢。 什么可能是错的？ 也许索引坏了？ 服务器：Debian，8GB 4x Intel（R）Xeon（R）CPU E3-1220 V2 @ 3.10GHz
表结构：
base=> d u_user
Table "public.u_user"
Column | Type | Modifiers
u_ip | character varying |
u_agent | text |
u_agent_js | text |
u_resolution_id | integer |
u_os | character varying |
u_os_id | smallint |
u_platform | character varying |
u_language | character varying |
u_language_id | smallint |
u_language_js | character varying |
u_cookie | smallint |
u_java | smallint |
u_color_depth | integer |
u_flash | character varying |
u_charset | character varying |
u_doctype | character varying |
u_compat_mode | character varying |
u_sex | character varying |
u_age | character varying |
u_theme | character varying |
u_behave | character varying |
u_targeting | character varying |
u_resolution | character varying |
u_user_hash | bigint |
u_tech_hash | character varying |
u_last_target_data_time | integer |
u_last_target_prof_time | integer |
u_id | bigint | not null default nextval('u_user_u_id_seq'::regclass)
u_sphinx | smallint | not null default 1::smallint
Indexes:
"u_user_u_id_pk" PRIMARY KEY, btree (u_id)
"u_user_hash_index" btree (u_user_hash)
"u_user_u_sphinx_ind" btree (u_sphinx)慢查询：
base=> explain analyze SELECT u_id FROM u_user WHERE u_sphinx = 1 LIMIT 1;
QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------
Limit (cost=0.00..0.15 rows=1 width=8) (actual time=485146.252..485146.252 rows=0 loops=1)
-> Seq Scan on u_user (cost=0.00..3023707.80 rows=19848860 width=8) (actual time=485146.249..485146.249 rows=0 loops=1)
Filter: (u_sphinx = 1)
Rows Removed by Filter: 23170476
Total runtime: 485160.241 ms
(5 rows)
解决了：
添加部分索引后
base=> explain analyze SELECT u_id FROM u_user WHERE u_sphinx = 1 LIMIT 1;
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------
Limit (cost=0.27..4.28 rows=1 width=8) (actual time=0.063..0.063 rows=0 loops=1)
-> Index Scan using u_user_u_sphinx_index_1 on u_user (cost=0.27..4.28 rows=1 width=8) (actual time=0.061..0.061 rows=0 loops=1)
Index Cond: (u_sphinx = 1)
Total runtime: 0.106 msThx为@Kouber Saparev
尝试制作部分索引。
CREATE INDEX u_user_u_sphinx_idx ON u_user (u_sphinx) WHERE u_sphinx = 1;
您的查询计划看起来像DB正在处理查询，就好像1在数据库中非常常见，以便挖掘到一个或两个磁盘以更好地识别相关行，而不是增加犁过的开销索引并在随机磁盘页面中查找行。
这可能表示您忘记运行以分析表格，以便规划者具有适当的统计信息：
analyze u_user