Postgres限制每个用户只能连接指定数量的session，防止服务器资源紧张

限制每个用户只能连接指定数量的session，防止服务器资源紧张

（1）创建测试用户test:

highgo=#create user test;
CREATEROLE
highgo=#\du
                             List of roles
 Role name |                   Attributes                   | Member of

-----------+------------------------------------------------+----------
 highgo   | Superuser, Create role, Create DB, Replication | {}
 test     |                                               | {}
（2）设置仅允许用户test使用一个连接

highgo=#ALTER ROLE test CONNECTION LIMIT 1;
ALTERROLE
（3）在session 1中使用test用户连接highgo数据库

highgo=>\c highgo  test
Youare now connected to database "highgo" as user "test".
highgo=>
（4）在session 2中也使用test用户连接highgo数据库，会出现如下错误：

highgo=#\c highgo  test
致命错误:  由角色"test"发起的连接太多了
Previousconnection kept
（5）查询用户test链接限制

highgo=>SELECT rolconnlimit FROM pg_roles WHERE rolname = 'test';
 rolconnlimit
--------------
            1
(1row)