postgresql – Postgres结合多个索引

CREATE TABLE test
(
   coords geography(Point,4326),user_id varchar(50),created_at timestamp
);
CREATE INDEX ix_coords ON test USING GIST (coords);
CREATE INDEX ix_user_id ON test (user_id);
CREATE INDEX ix_created_at ON test (created_at DESC);

这是我想要执行的查询：

select * 
from updates 
where ST_DWithin(coords,ST_MakePoint(-126.4,45.32)::geography,30000) 
and user_id='3212312' 
order by created_at desc
limit 60

当我运行查询时,它只使用ix_coords索引.如何确保Postgres使用ix_user_id和ix_created_at索引以及查询？

这是一个新表,我在其中批量插入生产数据.测试表中的总行数：15,069,489

我正在使用(effective_cache_size = 2GB)运行PostgreSQL 9.2.1(使用Postgis).这是我的本地OSX,具有16GB RAM,Core i7 / 2.5 GHz,非SSD磁盘.

添加EXPLAIN ANALYZE输出 –

Limit  (cost=71.64..71.65 rows=1 width=280) (actual time=1278.652..1278.665 rows=60 loops=1)
   ->  Sort  (cost=71.64..71.65 rows=1 width=280) (actual time=1278.651..1278.662 rows=60 loops=1)
         Sort Key: created_at
         Sort Method: top-N heapsort  Memory: 33kB
         ->  Index Scan using ix_coords on test  (cost=0.00..71.63 rows=1 width=280) (actual time=0.198..1278.227 rows=178 loops=1)
               Index Cond: (coords && '0101000020E61000006666666666E63C40C3F5285C8F824440'::geography)
               Filter: (((user_id)::text = '4f1092000b921a000100015c'::text) AND ('0101000020E61000006666666666E63C40C3F5285C8F824440'::geography && _st_expand(coords,30000::double precision)) AND _st_dwithin(coords,'0101000020E61000006666666666E63C40C3F5285C8F824440'::geography,30000::double precision,true))
               Rows Removed by Filter: 3122459
 Total runtime: 1278.701 ms

更新：

基于以下建议,我尝试使用索引user_id：

CREATE INDEX ix_coords_and_user_id ON updates USING GIST (coords,user_id);

..但是得到以下错误：

ERROR:  data type character varying has no default operator class for access method "gist"
HINT:  You must specify an operator class for the index or define a default operator class for the data type.

更新：

所以CREATE EXTENSION btree_gist;解决了btree / gist复合索引问题.现在我的索引看起来像

CREATE INDEX ix_coords_user_id_created_at ON test USING GIST (coords,user_id,created_at);

注意：btree_gist不接受DESC / ASC.

新的查询计划：

Limit  (cost=134.99..135.00 rows=1 width=280) (actual time=273.282..273.292 rows=60 loops=1)
   ->  Sort  (cost=134.99..135.00 rows=1 width=280) (actual time=273.281..273.285 rows=60 loops=1)
         Sort Key: created_at
         Sort Method: quicksort  Memory: 41kB
         ->  Index Scan using ix_updates_coords_user_id_created_at on updates  (cost=0.00..134.98 rows=1 width=280) (actual time=0.406..273.110 rows=115 loops=1)
               Index Cond: ((coords && '0101000020E61000006666666666E63C40C3F5285C8F824440'::geography) AND ((user_id)::text = '4e952bb5b9a77200010019ad'::text))
               Filter: (('0101000020E61000006666666666E63C40C3F5285C8F824440'::geography && _st_expand(coords,true))
               Rows Removed by Filter: 1
 Total runtime: 273.331 ms

查询比以前表现更好,几乎一秒钟更好,但仍然不是很好.我想这是我能得到的最好的？我希望在60-80ms左右.同样从查询中获取created_at desc的顺序,另外100ms,这意味着它无法使用索引.有任何解决这个问题的方法吗？