我在查找更多信息如何修改Postgres 9..0查询计划。修改Postgres 9.0查询计划
我有查询:
SELECT
max(creation_date)
FROM
statistics_loged_users
WHERE
school_id = 338 and
group_id = 3 and
usr_id = 243431;
和解释分析输出:
"Aggregate (cost=1518.56..1518.57 rows=1 width=8) (actual time=410.459..410.459 rows=1 loops=1)"
" -> Bitmap Heap Scan on statistics_loged_users (cost=993.96..1518.55 rows=1 width=8) (actual time=410.025..410.406 rows=210 loops=1)"
" Recheck Cond: ((group_id = 3) AND (usr_id = 243431))"
" Filter: (school_id = 338)"
" -> BitmapAnd (cost=993.96..993.96 rows=133 width=0) (actual time=409.521..409.521 rows=0 loops=1)"
" -> Bitmap Index Scan on statistics_loged_users_idx2 (cost=0.00..496.85 rows=26669 width=0) (actual time=375.770..375.770 rows=3050697 loops=1)"
" Index Cond: (group_id = 3)"
" -> Bitmap Index Scan on statistics_loged_users_idx (cost=0.00..496.85 rows=26669 width=0) (actual time=0.077..0.077 rows=210 loops=1)"
" Index Cond: (usr_id = 243431)"
"Total runtime: 411.419 ms"
我们可以看到,第一滤波器是GROUP_ID。 这个表格非常大:) 所以有很多行,其中group_id是相同的,但是具有相同usr_id的行少得多。
问题是我怎么能告诉查询计划,第一个过滤器必须是usr_id。
我创建GROUP_ID和usr_id指数和我的表现, 但我需要知道如何修改查询计划,这对未来:)
估计行26,669,实际3,050,697。我认为“真空分析”是有序的。你经常这样做吗? – 2012-02-28 01:01:37