停止数据库的命令：
1pg_ctl stop -D $PGDATA [-m shutdown-mode]
shutdown-mode有如下几种模式：
1. smart: 等所有的连接中止后，关闭数据库。如果客户端连接不终止， 则无法关闭数据库。
开启一个空会话：
[root@localhost ~]# su - postgres
[postgres@localhost ~]$ psql
psql (9.4.4)
Type "help" for help.
postgres=#
用smart关闭数据库：
[postgres@localhost ~]$ pg_ctl stop -D $PGDATA -m smart
waiting for server to shut down............................................................... failed
pg_ctl: server does not shut down
HINT: The "-m fast" option immediately disconnects sessions rather than
waiting for session-initiated disconnection
2. fast: 快速关闭数据库， 断开客户端的连接，让已有的事务回滚，然后正常关闭数据库。
[postgres@localhost ~]$ pg_ctl stop -D $PGDATA -m fast
waiting for server to shut down.... done
server stopped
查看关闭日志：
LOG: received fast shutdown request
LOG: aborting any active transactions
FATAL: terminating connection due to administrator command
LOG: shutting down
LOG: database system is shut down
会话被强制中断，然后关闭数据库。
起一个事务，然后测试关闭：
postgres=# create table t(id int primary key, name varchar(9));
CREATE TABLE
postgres=# begin;
BEGIN
postgres=# insert into t values(1,'a')
postgres-# ;
INSERT 0 1
不提交， 然后用FAST MODE去关闭数据库：
[postgres@localhost ~]$ pg_ctl stop -D $PGDATA -m fast
waiting for server to shut down.... done
server stopped
查看日志：
LOG: received fast shutdown request
LOG: aborting any active transactions
LOG: autovacuum launcher shutting down
FATAL: terminating connection due to administrator command
LOG: shutting down
LOG: database system is shut down
同样是直接中断会话， 而不去管事务有没有提交。
postgres=# select * from t;
id | name
----+------
(0 rows)
没有提交的数据， 在重启之后并不能查到。
3. immediate: 立即关闭数据库，立即停止数据库进程，直接退出，下次启动时会进行实例恢复。
postgres=# insert into t values(1,'a')
;
INSERT 0 1
postgres=# select * from t;
id | name
----+------
1 | a
(1 row)
关闭数据库：
[postgres@localhost ~]$ pg_ctl stop -D $PGDATA -m immediate
waiting for server to shut down.... done
server stopped
查看日志：
LOG: received immediate shutdown request
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.
