pg_cancel_backend() 与pg_terminate_backend()

先看下两个函数的官方解释：

 

 

pg_cancel_backend() 取消后台操作，回滚未提交事物

pg_terminate_backend() 中断session，回滚未提交事物

这里和oracle类似kill session的操作是pg_terminate_backend()

 

pg_cancel_backend()   举例：

session A:

postgres=# create table tb1 (a int); CREATE TABLE postgres=# begin;

postgres=# insert into tb1 select generate_series(1,100000000);

session B：

postgres=# select * from pg_stat_activity; datid | datname | procpid | usesysid | usename | application_name | client_addr | client_hostname | client_port | backend_start | xact_start | query_start | waiting | current_query -------+----------+---------+----------+----------+------------------+-------------+-----------------+-------------+-------------------------------+-------------------- -----------+-------------------------------+---------+------------------------------------------------------ 12699 | postgres | 10305 | 10 | postgres | psql | | | -1 | 2013-12-03 14:38:05.887116+08 | 2013-12-03 15:12:17 .773935+08 | 2013-12-03 15:14:31.454816+08 | f | insert into tb1 select generate_series(1,100000000);

postgres=# select pg_cancel_backend(10305); pg_cancel_backend ------------------- t

session A： ERROR: canceling statement due to user request postgres=# commit; ROLLBACK postgres=# select * from tb1; a --- (0 rows)

session B:

postgres=# select * from pg_stat_activity; datid | datname | procpid | usesysid | usename | application_name | client_addr | client_hostname | client_port | backend_start | xact_start | query_start | waiting | current_query -------+----------+---------+----------+----------+------------------+-------------+-----------------+-------------+-------------------------------+-------------------- -----------+-------------------------------+---------+--------------------------------- 12699 | postgres | 10305 | 10 | postgres | psql | | | -1 | 2013-12-03 14:38:05.887116+08 |

pg_terminate_backend() 举例：

session A：

postgres=# create table tb2 (a int); CREATE TABLE postgres=# begin; BEGIN postgres=# insert into tb2 select generate_series(1,100000000);

session B：

postgres=# select * from pg_stat_activity; datid | datname | procpid | usesysid | usename | application_name | client_addr | client_hostname | client_port | backend_start | xact_start | query_start | waiting | current_query -------+----------+---------+----------+----------+------------------+-------------+-----------------+-------------+-------------------------------+-------------------- -----------+-------------------------------+---------+------------------------------------------------------ 12699 | postgres | 10305 | 10 | postgres | psql | | | -1 | 2013-12-03 14:38:05.887116+08 | 2013-12-03 15:24:22 .45073+08 | 2013-12-03 15:24:33.362185+08 | f | insert into tb2 select generate_series(1,100000000);

postgres=# select pg_terminate_backend(10305); pg_terminate_backend ---------------------- t (1 row)

session A：

postgres=# insert into tb2 select generate_series(1,100000000); FATAL: terminating connection due to administrator command FATAL: terminating connection due to administrator command The connection to the server was lost. Attempting reset: Succeeded. postgres=# commit; WARNING: there is no transaction in progress COMMIT postgres=# select * from tb2; a --- (0 rows)

postgres=# select * from pg_stat_activity;

datid | datname | procpid | usesysid | usename | application_name | client_addr | client_hostname | client_port | backend_start | xact_start | query_start | waiting | current_query -------+----------+---------+----------+----------+------------------+-------------+-----------------+-------------+-------------------------------+-------------------- -----------+-------------------------------+---------+--------------------------------- 12699 | postgres | 10918 | 10 | postgres | psql | | | -1 | 2013-12-03 15:25:12.613672+08 | 2013-12-03 15:30:29 .544088+08 | 2013-12-03 15:30:29.544088+08 | f | select * from pg_stat_activity;

通过以上实验理解起来应该 很简单了，procpid= 10305在pg_cancel_backend()下，session还在，事物回退，在pg_terminate_backend()操作后，session消失，事物回退。如果在某些时候pg_terminate_backend()不能杀死session，那么可以在os层面，直接kill -9  pid