作者
digoal
日期
2020-01-01
标签
PostgreSQL , NOT IN , ANTI JOIN
背景
not in 转换为 anti join
https://commitfest.postgresql.org/26/2023/
https://www.postgresql.org/message-id/flat/1550706289606-0.post@n3.nabble.com
```
Hey, here is our latest patch. Major changes in this patch include:
1. Use the original hashed subplan if the inner fits in memory as decided by subplan_is_hashable().
2. Fixed the inner relation empty case by adding an inner relation existence check when we pull x out as a filter on the outer (see details below).
3. Integrate David Rowley's routine to use strict predicates and inner join conditions when checking nullability of a Var.
Detailed description of the patch:
NOT IN to ANTI JOIN transformation
If the NOT IN subquery is not eligible for hashed subplan as decided by
subplan_is_hashable(), do the following NOT IN to ANTI JOIN
transformation:
Single expression:
When x is nullable:
t1.x not in (t2.y where p) =>
ANTI JOIN
t1 (Filter: t1.x IS NOT NULL or NOT EXISTS (select 1 from t2 where p)),
t2 on join condition (t1.x=t2.y or t2.y IS NULL)
and p.
The predicate "t2.y IS NULL" can be removed if y is non-nullable.
When x is non-nullable:
t1.x not in (t2.y where p) =>
ANTI JOIN t1, t2 on join condition (t1.x=t2.y or t2.y IS NULL)
and p.
The predicate "t2.y IS NULL" can be removed if y is non-nullable.
Multi expression:
If all xi's are nullable:
(x1, x2, ... xn) not in (y1, y2, ... yn ) =>
ANTI JOIN t1, t2 on join condition:
((t1.x1 = t2.y1) and ... (t1.xi = t2.yi) ... and
(t1.xn = t2.yn)) IS NOT FALSE.
If at least one xi is non-nuallable:
(x1, x2, ... xn) not in (y1, y2, ... yn ) =>
ANTI JOIN t1, t2 on join condition:
(t1.x1 = t2.y1 or t2.y1 IS NULL or t1.x1 IS NULL) and ...
(t1.xi = t2.yi or t2.yi IS NULL) ... and
(t1.xn = t2.yn or t2.yn IS NULL or t1.xn IS NULL).
Add nullability testing routine is_node_nonnullable(), currently it
handles Var, TargetEntry, CoalesceExpr and Const. It uses strict
predicates, inner join conditions and NOT NULL constraint to check
the nullability of a Var.
Adjust and apply reduce_outer_joins() before the transformation so
that the outer joins have an opportunity to be converted to inner joins
prior to the transformation.
We measured performance improvements of two to five orders of magnitude
on most queries in a development environment. In our performance experiments,
table s (small) has 11 rows, table l (large) has 1 million rows. s.n and l.n
have NULL value. s.nn and l.nn are NOT NULL. Index is created on each column.
Cases using hash anti join:
l.nn not in (l.nn) 21900s -> 235ms
l.nn not in (l.nn where u>0) 22000s -> 240ms
l.n not in (l.nn) 21900s -> 238ms
l.n not in (l.nn where u>0) 22000s -> 248ms
Cases using index nested loop anti join
s.n not in (l.nn) 360ms -> 0.5ms
s.n not in (l.nn where u>0) 390ms -> 0.6ms
s.nn not in (l.nn) 365ms -> 0.5ms
s.nn not in (l.nn where u>0) 390ms -> 0.5ms
Cases using bitmap heap scan on the inner and nested loop anti join:
s.n not in (l.n) 360ms -> 0.7ms
l.n not in (l.n) 21900s -> 1.6s
l.n not in (l.n where u>0) 22000s -> 1680ms
s.nn not in (l.n) 360ms -> 0.5ms
l.nn not in (l.n) 21900s -> 1650ms
l.nn not in (l.n where u>0) 22000s -> 1660ms
Cases using the original hashed subplan:
l.n not in (s.n) 63ms -> 63ms
l.nn not in (s.nn) 63ms -> 63ms
l.n not in (s.n where u>0) 63ms -> 63ms
Comments are welcome.
Regards,
Zheng Li
AWS, Amazon Aurora PostgreSQL
```
参考
https://www.postgresql.org/message-id/flat/20190621185207.GA27929@alvherre.pgsql
https://commitfest.postgresql.org/26/2164/
PostgreSQL 许愿链接
您的愿望将传达给PG kernel hacker、数据库厂商等, 帮助提高数据库产品质量和功能, 说不定下一个PG版本就有您提出的功能点. 针对非常好的提议，奖励限量版PG文化衫、纪念品、贴纸、PG热门书籍等，奖品丰富，快来许愿。开不开森.
9.9元购买3个月阿里云RDS PostgreSQL实例
PostgreSQL 解决方案集合
德哥 / digoal's github - 公益是一辈子的事.
