本篇内容主要讲解“怎么使用PostgreSQL 12的settings选项”，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习“怎么使用PostgreSQL 12的settings选项”吧!
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PostgreSQL 12为explain命令提供了settings选项,可查看影响执行计划的设置修改.
测试数据:
testdb=# drop table if exists t_settings;
NOTICE: table "t_settings" does not exist, skipping
DROP TABLE
testdb=# create table t_settings(id int,c1 varchar(20));
CREATE TABLE
testdb=#
testdb=# insert into t_settings select x,'c1'||x from generate_series(1,100000) as x;
INSERT 0 100000
testdb=# create index idx_t_settings_id on t_settings(id);
CREATE INDEX
PG 11
testdb=# explain (settings on) select * from t_settings where id = 1;
ERROR: unrecognized EXPLAIN option "settings"
LINE 1: explain (settings on) select * from t_settings where id = 1;
^
PG 11不支持该特性.
PG 12
PG 12新增了该特性
[local]:5432 pg12@testdb=# explain (settings on) select * from t_settings where id = 1;
QUERY PLAN
-----------------------------------------------------------------------------------
Bitmap Heap Scan on t_settings (cost=12.17..570.66 rows=500 width=62)
Recheck Cond: (id = 1)
-> Bitmap Index Scan on idx_t_settings_id (cost=0.00..12.04 rows=500 width=0)
Index Cond: (id = 1)
(4 rows)
Time: 5.403 ms
修改参数,查看执行计划
[local]:5432 pg12@testdb=# set enable_indexscan=off;
SET
Time: 0.555 ms
[local]:5432 pg12@testdb=# explain (settings on) select * from t_settings where id = 1;
QUERY PLAN
--------------------------------------------------------------------------------
Bitmap Heap Scan on t_settings (cost=4.30..8.31 rows=1 width=11)
Recheck Cond: (id = 1)
-> Bitmap Index Scan on idx_t_settings_id (cost=0.00..4.30 rows=1 width=0)
Index Cond: (id = 1)
Settings: enable_indexscan = 'off'
(5 rows)
Time: 0.759 ms
注意执行计划中的” Settings: enable_indexscan = ‘off’ “,把影响执行计划的参数修改打印出来,这是一个pretty cool特性,增强了易用性.
到此，相信大家对“怎么使用PostgreSQL 12的settings选项”有了更深的了解，不妨来实际操作一番吧！这里是创新互联网站，更多相关内容可以进入相关频道进行查询，关注我们，继续学习！
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