Процессы операционной системы

postgres$ ps -o pid,command --ppid `head -n 1 $PGDATA/postmaster.pid`
  PID COMMAND
10810 postgres: 9.6/main: checkpointer process   
10811 postgres: 9.6/main: writer process   
10812 postgres: 9.6/main: wal writer process   
10813 postgres: 9.6/main: autovacuum launcher process   
10814 postgres: 9.6/main: stats collector process   
30953 postgres: 9.6/main: autovacuum worker process   plpgsql_exceptions

К процессам, обслуживающим буферный кэш и журнал, можно отнести:

Остановка в режиме fast

postgres$ rm /var/log/postgresql/postgresql-9.6-main.log
student$ sudo pg_ctlcluster 9.6 main restart

Журнал сообщений сервера:

postgres$ cat /var/log/postgresql/postgresql-9.6-main.log
2017-08-25 22:15:54 MSK [2349-1] LOG:  database system was shut down at 2017-08-25 22:15:52 MSK
2017-08-25 22:15:54 MSK [2349-2] LOG:  MultiXact member wraparound protections are now enabled
2017-08-25 22:15:54 MSK [2348-1] LOG:  database system is ready to accept connections
2017-08-25 22:15:54 MSK [2353-1] LOG:  autovacuum launcher started
2017-08-25 22:15:54 MSK [2357-1] [unknown]@[unknown] LOG:  incomplete startup packet

Остановка в режиме immediate

postgres$ rm /var/log/postgresql/postgresql-9.6-main.log
student$ sudo pg_ctlcluster 9.6 main stop -m immediate --skip-systemctl-redirect
student$ sudo pg_ctlcluster 9.6 main restart

Журнал сообщений сервера:

postgres$ cat /var/log/postgresql/postgresql-9.6-main.log
2017-08-25 22:15:56 MSK [2429-1] LOG:  database system was interrupted; last known up at 2017-08-25 22:15:54 MSK
2017-08-25 22:15:56 MSK [2430-1] [unknown]@[unknown] LOG:  incomplete startup packet
2017-08-25 22:15:57 MSK [2429-2] LOG:  database system was not properly shut down; automatic recovery in progress
2017-08-25 22:15:57 MSK [2429-3] LOG:  invalid record length at F/60A7A35C: wanted 24, got 0
2017-08-25 22:15:57 MSK [2429-4] LOG:  redo is not required
2017-08-25 22:15:57 MSK [2433-1] postgres@postgres FATAL:  the database system is starting up
2017-08-25 22:15:57 MSK [2429-5] LOG:  MultiXact member wraparound protections are now enabled
2017-08-25 22:15:57 MSK [2428-1] LOG:  database system is ready to accept connections
2017-08-25 22:15:57 MSK [2437-1] LOG:  autovacuum launcher started

Перед тем, как начать принимать соединения, СУБД выполнила восстановление (automatic recovery in progress).