PostgreSQL三种关闭方式的区别

1、使用smart参数关闭数据库:
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。
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。
[postgresql@master ~]$ pg_ctl stop -D $PGDATA -m smart
waiting for server to shut down.... done
server stopped
[postgresql@master ~]$

使用smart参数关闭数据库的日志：
2025-09-06 19:40:20.479 CST [56233] LOG:  received smart shutdown request
2025-09-06 19:40:20.480 CST [56233] LOG:  background worker "logical replication launcher" (PID 56241) exited with exit code 1
2025-09-06 19:40:20.480 CST [56236] LOG:  shutting down
2025-09-06 19:40:20.485 CST [56233] LOG:  database system is shut down

2、使用fast参数关闭数据库:
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。
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。
[postgresql@master ~]$ pg_ctl stop -D $PGDATA -m fast
waiting for server to shut down.... done
server stopped
[postgresql@master ~]

使用fast参数关闭数据库的日志：
2025-09-06 19:40:59.477 CST [56258] LOG:  received fast shutdown request
2025-09-06 19:40:59.478 CST [56258] LOG:  aborting any active transactions
2025-09-06 19:40:59.478 CST [56258] LOG:  background worker "logical replication launcher" (PID 56266) exited with exit code 1
2025-09-06 19:40:59.479 CST [56261] LOG:  shutting down
2025-09-06 19:40:59.484 CST [56258] LOG:  database system is shut down

3、使用immediate参数关闭数据库:
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。
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。
[postgresql@master ~]$ pg_ctl stop -D $PGDATA -m immediate
waiting for server to shut down.... done
server stopped
[postgresql@master ~]$

使用immediate参数关闭数据库的日志：
2025-09-06 19:41:40.311 CST [56278] LOG:  received immediate shutdown request
2025-09-06 19:41:40.313 CST [56284] WARNING:  terminating connection because of crash of another server process
2025-09-06 19:41:40.313 CST [56284] 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.
2025-09-06 19:41:40.313 CST [56284] HINT:  In a moment you should be able to reconnect to the database and repeat your command.
2025-09-06 19:41:40.315 CST [56278] LOG:  database system is shut down

4、数据目录：
[postgresql@master ~]$ echo $PGDATA
/usr/local/postgresql/data

5、启动数据库：
[postgresql@master ~]$ pg_ctl start -D $PGDATA
waiting for server to start....2025-09-06 19:40:40.221 CST [56258] LOG:  redirecting log output to logging collector process
2025-09-06 19:40:40.221 CST [56258] HINT:  Future log output will appear in directory "log".
done
server started
[postgresql@master ~]$