kill -9 a postgres process

　　在postgresql中，不推荐使用Kill -9直接杀掉异常连接，因为直接使用kill -9会引起整个数据库核心进程的重启，同时其他正常程序连接也会被杀掉。

　　现开启两个psql连接，然后使用Kill -9杀掉其中一个：

session1: 

swrd=# select pg_backend_pid();
 pg_backend_pid
----------------
          26965
(1 row)

swrd=# select pg_backend_pid();
WARNING:  terminating connection because of crash of another server process
DETAIL:  The postmaster has commanded this server process to roll back the current transaction and exit, 
because another server process exited abnormally and possibly corrupted shared memory.
HINT:  In a moment you should be able to reconnect to the database and repeat your command.
server closed the connection unexpectedly
    This probably means the server terminated abnormally
    before or while processing the request.
The connection to the server was lost. Attempting reset: Succeeded.
swrd=# select pg_backend_pid();
 pg_backend_pid
----------------
            833
(1 row)

session2:

postgres=# select pg_backend_pid();
 pg_backend_pid
----------------
          25975
(1 row)

postgres=# select pg_backend_pid();
server closed the connection unexpectedly
    This probably means the server terminated abnormally
    before or while processing the request.
The connection to the server was lost. Attempting reset: Succeeded.
postgres=# select pg_backend_pid();
 pg_backend_pid
----------------
            835
(1 row)

观察上面的日志信息，可以看到session2是被杀掉的会话，但同时session1也被杀掉了。

下面是有关postgre的进程信息，发现除了守护进程和logger进程外，其他进程都重启了。

[root@db~]# ps auxwwf |grep postgres
root       0.0  0.0    pts/    S    :   :  |       \_ su - postgres
postgres   0.0  0.0    pts/    S    :   :  |           \_ -bash
postgres   0.0  0.0    pts/    S+   :   :  |               \_ psql
root       0.0  0.0    pts/    S    :   :  |       \_ su - postgres
postgres   0.0  0.0    pts/    S    :   :  |           \_ -bash
postgres   0.0  0.0    pts/    S+   :   :  |               \_ psql
root         0.0  0.0     pts/    S+   :   :          \_ grep postgres
postgres    0.0  0.0    ?        S        : /opt/pg96/bin/postgres
postgres    0.0  0.0    ?        Ss       :  \_ postgres: logger process
postgres   0.0  0.0    ?        Ss   :   :  \_ postgres: checkpointer process
postgres   0.0  0.0    ?        Ss   :   :  \_ postgres: writer process
postgres   0.0  0.0    ?        Ss   :   :  \_ postgres: wal writer process
postgres   0.0  0.0    ?        Ss   :   :  \_ postgres: autovacuum launcher process
postgres   0.0  0.0    ?        Ss   :   :  \_ postgres: archiver process
postgres   0.0  0.0    ?        Ss   :   :  \_ postgres: stats collector process
postgres   0.0  0.0    ?        Ss   :   :  \_ postgres: postgres postgres [local] idle
postgres   0.0  0.0    ?        Ss   :   :  \_ postgres: swrd swrd [local] idle
[root@db~]# kill -
[root@db~]# ps auxwwf |grep postgres
root       0.0  0.0    pts/    S    :   :  |       \_ su - postgres
postgres   0.0  0.0    pts/    S    :   :  |           \_ -bash
postgres   0.0  0.0    pts/    S+   :   :  |               \_ psql
root       0.0  0.0    pts/    S    :   :  |       \_ su - postgres
postgres   0.0  0.0    pts/    S    :   :  |           \_ -bash
postgres   0.0  0.0    pts/    S+   :   :  |               \_ psql
root         0.0  0.0     pts/    S+   :   :          \_ grep postgres
postgres    0.0  0.0    ?        S        : /opt/pg96/bin/postgres
postgres    0.0  0.0    ?        Ss       :  \_ postgres: logger process
postgres     0.0  0.0    ?        Ss   :   :  \_ postgres: checkpointer process
postgres     0.0  0.0    ?        Ss   :   :  \_ postgres: writer process
postgres     0.0  0.0    ?        Ss   :   :  \_ postgres: wal writer process
postgres     0.0  0.0    ?        Ss   :   :  \_ postgres: autovacuum launcher process
postgres     0.0  0.0    ?        Ss   :   :  \_ postgres: archiver process
postgres     0.0  0.0    ?        Ss   :   :  \_ postgres: stats collector process 

　　postgres之所以这么做是因为使用kill -9杀掉的进程，是没有机会做好清理工作的，因为kill -9是SIGKILL信号，程序不属于正常退出，杀掉的进程可能由于正在进行写入或修改的操作，从而造成内存页的损坏，为了保证数据库的正常故会重启内部进程。

　　如果不使用kill -9，而使用普通的kill操作是不会引起postgres内部进程的重启的。对于中断操作或杀掉会话，建议使用pg自带的pg_cancel_backend()和pg_terminate_backend()。

参考:

https://serverfault.com/questions/415188/kill-9-a-postgres-process