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 $PGDATA -m immediate
waiting for server to shut down…. done
server stopped
查看日志：
LOG: received immediate shutdown request
WARNING: terminating connection because of crash of another server process
DETAIL: The postmaster has commanded this server process to roll back the current transaction and exit, because another server process exited abnormally and possibly corrupted shared memory.
HINT: In a moment you should be able to reconnect to the database and repeat your command.
WARNING: terminating connection because of crash of another server process
DETAIL: The postmaster has commanded this server process to roll back the current transaction and exit, because another server process exited abnormally and possibly corrupted shared memory.
HINT: In a moment you should be able to reconnect to the database and repeat your command.
启动数据库：
[postgres@localhost ~]$ pg_ctl -D /apps/pgsql/pgdata -l 1.log start
server starting
查看日志：
LOG: database system was interrupted; last known up at 2017-04-27 18:56:47 PDT
LOG: database system was not properly shut down; automatic recovery in progress #提示非正常关机，自动开启恢复。
LOG: redo starts at 0/181F910
LOG: record with zero length at 0/181FA90
LOG: redo done at 0/181FA60
LOG: last completed transaction was at log time 2017-04-27 18:59:13.727213-07
LOG: MultiXact member wraparound protections are now enabled
LOG: autovacuum launcher started
LOG: database system is ready to accept connections
查看数据：
[postgres@localhost ~]$ psql
psql (9.4.4)
Type "help" for help.
postgres=# select * from t;
id | name
—-+——
1 | a
(1 row)
提交的数据已通过实例恢复。
小结：
对比以上三种关库模式：
smart最为安全，但最慢， 需要将所有连接都断开后，才会关库，默认关库模式。
fast强制中断会话，而不管有操作有没有提交，在做系统维护（系统维护时一般应用都正常关闭了，或者不再会有事务操作。）时，需要这种模式来关闭数据库。
immediate最暴力的方式，不管数据有没有落盘（POSGRE是遵循WAL机制），就直接关掉， 待启动时进行实例恢复， 如果在关库前有大量的事务没有写入磁盘， 那这个恢复过程可能会非常的漫长。
补充：postgresql 异步 stream replication 环境关闭 master 的验证
os: ubuntu 16.04
db: postgresql 9.6.8
验证在异步 stream replication环境下，主动关闭master时，数据是否有丢失，能丢失多少。
版本
# lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 16.04.5 LTS
Release: 16.04
Codename: xenial
# su – postgres -c "psql -c \"select version();\""
version
———————————————————————————————————————————————-
PostgreSQL 9.6.8 on x86_64-pc-linux-gnu (Ubuntu 9.6.8-1.pgdg16.04+1), compiled by gcc (Ubuntu 5.4.0-6ubuntu1~16.04.9) 5.4.0 20160609, 64-bit
(1 row)
用 pgbench 模拟数据库的大量数据操作
postgres=# create database pgbenchdb;
# su – postgres
$ pgbench -i -s 20 pgbenchdb
$ pgbench -r -j2 -c4 -T300 pgbenchdb
关闭 master
# su – postgres
$ /usr/lib/postgresql/9.6/bin/pg_ctl stop -m fast -D "/data/pg9.6/main"
提升 slave
# su – postgres
$ /usr/lib/postgresql/9.6/bin/pg_ctl promote -D "/data/pg9.6/main"
查看 old master 的 xlog location
$ /usr/lib/postgresql/9.6/bin/pg_xlogdump 000000010000000000000016
rmgr: XLOG len (rec/tot): 106/ 106, tx: 0, lsn: 0/16000028, prev 0/152C9A10, desc: CHECKPOINT_SHUTDOWN redo 0/16000028; tli 1; prev tli 1; fpw true; xid 0:118746; oid 16432; multi 1; offset 0; oldest xid 543 in DB 1; oldest multi 1 in DB 1; oldest/newest commit timestamp xid: 550/118745; oldest running xid 0; shutdown
pg_xlogdump: FATAL: error in WAL record at 0/16000028: invalid record length at 0/16000098: wanted 24, got 0
可以看到 lsn: 0/16000028, prev 0/152C9A10, desc: CHECKPOINT_SHUTDOWN redo 0/16000028;
查看 new master 的 .history文件
$ ls -lt|more
total 360456
-rw——- 1 postgres postgres 16777216 Nov 30 10:32 000000020000000000000016
drwx—— 2 postgres postgres 4096 Nov 30 10:16 archive_status
-rw——- 1 postgres postgres 42 Nov 30 10:16 00000002.history
-rw——- 1 postgres postgres 16777216 Nov 30 10:16 000000010000000000000016.partial
-rw——- 1 postgres postgres 16777216 Nov 30 10:16 000000010000000000000015
-rw——- 1 postgres postgres 16777216 Nov 30 10:16 000000010000000000000014
-rw——- 1 postgres postgres 16777216 Nov 30 10:05 000000010000000000000013
$ cat 00000002.history
1 0/16000098 no recovery target specified
$ /usr/lib/postgresql/9.6/bin/pg_xlogdump 000000010000000000000016
rmgr: XLOG len (rec/tot): 106/ 106, tx: 0, lsn: 0/16000028, prev 0/152C9A10, desc: CHECKPOINT_SHUTDOWN redo 0/16000028; tli 1; prev tli 1; fpw true; xid 0:118746; oid 16432; multi 1; offset 0; oldest xid 543 in DB 1; oldest multi 1 in DB 1; oldest/newest commit timestamp xid: 550/118745; oldest running xid 0; shutdown
rmgr: XLOG len (rec/tot): 42/ 42, tx: 0, lsn: 0/16000098, prev 0/16000028, desc: END_OF_RECOVERY tli 2; prev tli 1; time 2018-11-30 10:16:57.249408 CST
rmgr: Standby len (rec/tot): 50/ 50, tx: 0, lsn: 0/160000C8, prev 0/16000098, desc: RUNNING_XACTS nextXid 118746 latestCompletedXid 118745 oldestRunningXid 118746
rmgr: XLOG len (rec/tot): 51/ 312, tx: 0, lsn: 0/16000100, prev 0/160000C8, desc: FPI_FOR_HINT , blkref #0: rel 1664/0/1260 blk 0 FPW
rmgr: Standby len (rec/tot): 50/ 50, tx: 0, lsn: 0/16000238, prev 0/16000100, desc: RUNNING_XACTS nextXid 118746 latestCompletedXid 118745 oldestRunningXid 118746
pg_xlogdump: FATAL: error in WAL record at 0/16000238: invalid record length at 0/16000270: wanted 24, got 0
