Tag Archives: PostgreSQL for DBAs

Types of Shutdown in PostgreSQL

Types of Shutdown in PostgreSQL

PostgreSQL Shutdown TypeOracleBehavior
Smart (SIGTERM)SHUTDOWN NORMALThe server stops accepting new connections but allows existing sessions to continue running normally. PostgreSQL shuts down only after all active sessions disconnect and their transactions complete successfully.
Fast (SIGINT – Default)SHUTDOWN IMMEDIATEThe server stops accepting new connections and immediately terminates all active sessions. Any uncommitted transactions are rolled back, and PostgreSQL performs a clean shutdown gracefully.
Immediate (SIGQUIT)SHUTDOWN ABORTThe server terminates all processes instantly without performing a proper shutdown. No cleanup or checkpoint occurs, so PostgreSQL performs crash recovery by replaying WAL files during the next startup.
Shutdown TypeSignalCommand ExampleBehavior
SmartSIGTERMpg_ctl stop -D /pgData -m smartStops new connections, waits for existing sessions to finish normally, then shuts down.
Fast (Default)SIGINTpg_ctl stop -D /pgdata -m fastStops new connections, terminates active sessions, rolls back uncommitted transactions, and shuts down cleanly.
ImmediateSIGQUITpg_ctl stop -D /pgdata -m immediateStops immediately without proper shutdown. Recovery from WAL files happens during next startup.

Difference Between Reload and Restart

  • When we change server configuration parameters, PostgreSQL needs to read those changes before they become active.
  • Reload applies the new configuration without stopping or restarting the database service. Existing connections and database activity continue normally.
  • Some configuration parameter changes cannot be applied through reload and will only take effect after a restart.
  • Restart stops the PostgreSQL server gracefully, ends all running activities, releases resources, closes open files, and then starts the server again with the new configuration.

 

Smart Shutdown (SIGTERM):

[postgres@pgdb02 ~]$ pg_ctl stop -D /pgData/pgsql17/data -m smart
waiting for server to shut down.... done
server stopped
[postgres@pgdb02 ~]$

2026-07-03 14:26:59.741 +08 [3476] LOG:  received smart shutdown request
2026-07-03 14:26:59.752 +08 [3476] LOG:  background worker "logical replication launcher" (PID 3483) exited with exit code 1
2026-07-03 14:26:59.753 +08 [3478] LOG:  shutting down
2026-07-03 14:26:59.755 +08 [3478] LOG:  checkpoint starting: shutdown immediate
2026-07-03 14:26:59.765 +08 [3478] LOG:  checkpoint complete: wrote 3 buffers (0.0%); 0 WAL file(s) added, 0 removed, 0 recycled; write=0.002 s, sync=0.003 s, total=0.012 s; sync files=2, longest=0.003 s, average=0.002 s; distance=0 kB, estimate=0 kB; lsn=1/105465F0, redo lsn=1/105465F0
2026-07-03 14:26:59.771 +08 [3476] LOG:  database system is shut down


[postgres@pgdb02 ~]$ pg_ctl start -D /pgData/pgsql17/data
waiting for server to start....2026-07-03 14:27:18.394 +08 [3487] LOG:  redirecting log output to logging collector process
2026-07-03 14:27:18.394 +08 [3487] HINT:  Future log output will appear in directory "log".
 done
server started
[postgres@pgdb02 ~]$

2026-07-03 14:27:18.394 +08 [3487] LOG:  starting PostgreSQL 17.10 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 11.5.0 20240719 (Red Hat 11.5.0-14), 64-bit
2026-07-03 14:27:18.396 +08 [3487] LOG:  listening on IPv4 address "0.0.0.0", port 5432
2026-07-03 14:27:18.396 +08 [3487] LOG:  listening on IPv6 address "::", port 5432
2026-07-03 14:27:18.399 +08 [3487] LOG:  listening on Unix socket "/run/postgresql/.s.PGSQL.5432"
2026-07-03 14:27:18.404 +08 [3487] LOG:  listening on Unix socket "/tmp/.s.PGSQL.5432"
2026-07-03 14:27:18.413 +08 [3491] LOG:  database system was shut down at 2026-07-03 14:26:59 +08
2026-07-03 14:27:18.425 +08 [3487] LOG:  database system is ready to accept connections

Fast Shutdown (SIGINT – Default):

[postgres@pgdb02 ~]$ pg_ctl stop -D /pgData/pgsql17/data -m fast
waiting for server to shut down.... done
server stopped
[postgres@pgdb02 ~]$

2026-07-03 14:28:26.839 +08 [3487] LOG:  received fast shutdown request
2026-07-03 14:28:26.844 +08 [3487] LOG:  aborting any active transactions
2026-07-03 14:28:26.854 +08 [3487] LOG:  background worker "logical replication launcher" (PID 3494) exited with exit code 1
2026-07-03 14:28:26.860 +08 [3489] LOG:  shutting down
2026-07-03 14:28:26.862 +08 [3489] LOG:  checkpoint starting: shutdown immediate
2026-07-03 14:28:26.874 +08 [3489] LOG:  checkpoint complete: wrote 3 buffers (0.0%); 0 WAL file(s) added, 0 removed, 0 recycled; write=0.002 s, sync=0.005 s, total=0.015 s; sync files=2, longest=0.004 s, average=0.003 s; distance=0 kB, estimate=0 kB; lsn=1/105466A0, redo lsn=1/105466A0
2026-07-03 14:28:26.882 +08 [3487] LOG:  database system is shut down

[postgres@pgdb02 ~]$ pg_ctl start -D /pgData/pgsql17/data
waiting for server to start....2026-07-03 14:29:00.574 +08 [3505] LOG:  redirecting log output to logging collector process
2026-07-03 14:29:00.574 +08 [3505] HINT:  Future log output will appear in directory "log".
 done
server started
[postgres@pgdb02 ~]$

2026-07-03 14:29:00.575 +08 [3505] LOG:  starting PostgreSQL 17.10 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 11.5.0 20240719 (Red Hat 11.5.0-14), 64-bit
2026-07-03 14:29:00.579 +08 [3505] LOG:  listening on IPv4 address "0.0.0.0", port 5432
2026-07-03 14:29:00.580 +08 [3505] LOG:  listening on IPv6 address "::", port 5432
2026-07-03 14:29:00.582 +08 [3505] LOG:  listening on Unix socket "/run/postgresql/.s.PGSQL.5432"
2026-07-03 14:29:00.587 +08 [3505] LOG:  listening on Unix socket "/tmp/.s.PGSQL.5432"
2026-07-03 14:29:00.595 +08 [3509] LOG:  database system was shut down at 2026-07-03 14:28:26 +08
2026-07-03 14:29:00.607 +08 [3505] LOG:  database system is ready to accept connections

Immediate Shutdown (SIGQUIT):

[postgres@pgdb02 ~]$ pg_ctl stop -D /pgData/pgsql17/data -m immediate
waiting for server to shut down.... done
server stopped
[postgres@pgdb02 ~]$

2026-07-03 14:29:47.471 +08 [3505] LOG:  received immediate shutdown request
2026-07-03 14:29:47.485 +08 [3505] LOG:  database system is shut down


[postgres@pgdb02 ~]$ pg_ctl start -D /pgData/pgsql17/data
waiting for server to start....2026-07-03 14:30:17.965 +08 [3520] LOG:  redirecting log output to logging collector process
2026-07-03 14:30:17.965 +08 [3520] HINT:  Future log output will appear in directory "log".
. done
server started
[postgres@pgdb02 ~]$

2026-07-03 14:30:17.966 +08 [3520] LOG:  starting PostgreSQL 17.10 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 11.5.0 20240719 (Red Hat 11.5.0-14), 64-bit
2026-07-03 14:30:17.966 +08 [3520] LOG:  listening on IPv4 address "0.0.0.0", port 5432
2026-07-03 14:30:17.966 +08 [3520] LOG:  listening on IPv6 address "::", port 5432
2026-07-03 14:30:17.970 +08 [3520] LOG:  listening on Unix socket "/run/postgresql/.s.PGSQL.5432"
2026-07-03 14:30:17.974 +08 [3520] LOG:  listening on Unix socket "/tmp/.s.PGSQL.5432"
2026-07-03 14:30:17.983 +08 [3524] LOG:  database system was interrupted; last known up at 2026-07-03 14:29:00 +08
2026-07-03 14:30:19.211 +08 [3524] LOG:  database system was not properly shut down; automatic recovery in progress
2026-07-03 14:30:19.216 +08 [3524] LOG:  redo starts at 1/10546718
2026-07-03 14:30:19.216 +08 [3524] LOG:  invalid record length at 1/10546750: expected at least 24, got 0
2026-07-03 14:30:19.217 +08 [3524] LOG:  redo done at 1/10546718 system usage: CPU: user: 0.00 s, system: 0.00 s, elapsed: 0.00 s
2026-07-03 14:30:19.221 +08 [3522] LOG:  checkpoint starting: end-of-recovery immediate wait
2026-07-03 14:30:19.231 +08 [3522] LOG:  checkpoint complete: wrote 3 buffers (0.0%); 0 WAL file(s) added, 0 removed, 0 recycled; write=0.002 s, sync=0.003 s, total=0.012 s; sync files=2, longest=0.002 s, average=0.002 s; distance=0 kB, estimate=0 kB; lsn=1/10546750, redo lsn=1/10546750
2026-07-03 14:30:19.239 +08 [3520] LOG:  database system is ready to accept connections

Caution: Your use of any information or materials on this website is entirely at your own risk. It is provided for educational purposes only. It has been tested internally, however, we do not guarantee that it will work for you. Ensure that you run it in your test environment before using.

Thank you,
Rajasekhar Amudala
Email: br8dba@gmail.com
Linkedin: https://www.linkedin.com/in/rajasekhar-amudala/

Create a Second PostgreSQL Instance on the Same Linux Server

Create a Second PostgreSQL Instance on the Same Linux Server

Table of Contents



0. Verify existing setup

[postgres@pgdb02 ~]$ ps -ef | grep postgres
root        3641    3561  0 16:57 pts/1    00:00:00 su - postgres
postgres    3642    3641  0 16:57 pts/1    00:00:00 -bash
postgres    3711       1  0 17:03 ?        00:00:00 /pgBin/pgsql/17.4/bin/postgres -D /pgData/pgsql/17.4
postgres    3712    3711  0 17:03 ?        00:00:00 postgres: PGDB_SIT: checkpointer
postgres    3713    3711  0 17:03 ?        00:00:00 postgres: PGDB_SIT: background writer
postgres    3715    3711  0 17:03 ?        00:00:00 postgres: PGDB_SIT: walwriter
postgres    3716    3711  0 17:03 ?        00:00:00 postgres: PGDB_SIT: autovacuum launcher
postgres    3717    3711  0 17:03 ?        00:00:00 postgres: PGDB_SIT: logical replication launcher
postgres    3731    3642  0 17:03 pts/1    00:00:00 psql
postgres    3732    3711  0 17:03 ?        00:00:00 postgres: PGDB_SIT: postgres postgres [local] idle
root        3748    3164  0 17:09 pts/0    00:00:00 su - postgres
postgres    3749    3748  0 17:09 pts/0    00:00:00 -bash
postgres    3911    3749  0 17:59 pts/0    00:00:00 ps -ef
postgres    3912    3749  0 17:59 pts/0    00:00:00 grep --color=auto postgres
[postgres@pgdb02 ~]$

1. Create new directories

[root@pgdb02 ~]# mkdir -p /pgData/pgsql/17.4/dev
[root@pgdb02 ~]# mkdir -p /pgWal/pgsql/17.4/dev
[root@pgdb02 ~]# chown -R postgres:postgres /pgData /pgWal
[root@pgdb02 ~]#

2. Initialize second cluster

# As postgres user 

[postgres@pgdb02 ~]$ /pgBin/pgsql/17.4/bin/initdb -D /pgData/pgsql/17.4/dev --waldir=/pgWal/pgsql/17.4/dev --wal-segsize=128
The files belonging to this database system will be owned by user "postgres".
This user must also own the server process.

The database cluster will be initialized with locale "en_SG.UTF-8".
The default database encoding has accordingly been set to "UTF8".
The default text search configuration will be set to "english".

Data page checksums are disabled.

fixing permissions on existing directory /pgData/pgsql/17.4/dev ... ok
fixing permissions on existing directory /pgWal/pgsql/17.4/dev ... ok
creating subdirectories ... ok
selecting dynamic shared memory implementation ... posix
selecting default "max_connections" ... 100
selecting default "shared_buffers" ... 128MB
selecting default time zone ... Asia/Singapore
creating configuration files ... ok
running bootstrap script ... ok
performing post-bootstrap initialization ... ok
syncing data to disk ... ok

initdb: warning: enabling "trust" authentication for local connections
initdb: hint: You can change this by editing pg_hba.conf or using the option -A, or --auth-local and --auth-host, the next time you run initdb.

Success. You can now start the database server using:

    /pgBin/pgsql/17.4/bin/pg_ctl -D /pgData/pgsql/17.4/dev -l logfile start

[postgres@pgdb02 ~]$

[postgres@pgdb02 ~]$ ls -ld /pgData/pgsql/17.4/dev
drwx------. 18 postgres postgres 4096 Jun 20 18:03 /pgData/pgsql/17.4/dev
[postgres@pgdb02 ~]$
[postgres@pgdb02 ~]$ ls -ltr /pgData/pgsql/17.4/dev
total 56
lrwxrwxrwx. 1 postgres postgres    21 Jun 20 18:03 pg_wal -> /pgWal/pgsql/17.4/dev
drwx------. 2 postgres postgres     6 Jun 20 18:03 pg_commit_ts
drwx------. 2 postgres postgres     6 Jun 20 18:03 pg_dynshmem
drwx------. 2 postgres postgres     6 Jun 20 18:03 pg_twophase
drwx------. 2 postgres postgres     6 Jun 20 18:03 pg_tblspc
drwx------. 2 postgres postgres     6 Jun 20 18:03 pg_stat_tmp
drwx------. 2 postgres postgres     6 Jun 20 18:03 pg_snapshots
drwx------. 2 postgres postgres     6 Jun 20 18:03 pg_serial
drwx------. 2 postgres postgres     6 Jun 20 18:03 pg_replslot
drwx------. 2 postgres postgres     6 Jun 20 18:03 pg_notify
drwx------. 4 postgres postgres    36 Jun 20 18:03 pg_multixact
-rw-------. 1 postgres postgres     3 Jun 20 18:03 PG_VERSION
-rw-------. 1 postgres postgres 30718 Jun 20 18:03 postgresql.conf
-rw-------. 1 postgres postgres    88 Jun 20 18:03 postgresql.auto.conf
-rw-------. 1 postgres postgres  5711 Jun 20 18:03 pg_hba.conf
-rw-------. 1 postgres postgres  2640 Jun 20 18:03 pg_ident.conf
drwx------. 2 postgres postgres    18 Jun 20 18:03 pg_xact
drwx------. 2 postgres postgres    18 Jun 20 18:03 pg_subtrans
drwx------. 2 postgres postgres  4096 Jun 20 18:03 global
drwx------. 5 postgres postgres    33 Jun 20 18:03 base
drwx------. 4 postgres postgres    68 Jun 20 18:03 pg_logical
drwx------. 2 postgres postgres    25 Jun 20 18:03 pg_stat
[postgres@pgdb02 ~]$

**** we can see here 700 permission set by initdb command.

3. Edit second instance config

[postgres@pgdb02 ~]$ egrep "^(#)?(port|cluster_name)" /pgData/pgsql/17.4/dev/postgresql.conf
#port = 5432                            # (change requires restart)
#cluster_name = ''                      # added to process titles if nonempty
[postgres@pgdb02 ~]$


[postgres@pgdb02 ~]$ cp /pgData/pgsql/17.4/dev/postgresql.conf /pgData/pgsql/17.4/dev/postgresql.conf.bkp
[postgres@pgdb02 ~]$

[postgres@pgdb02 ~]$ sed -i "s/^#port = 5432.*/port = 5433/" /pgData/pgsql/17.4/dev/postgresql.conf
[postgres@pgdb02 ~]$ sed -i "s/^#cluster_name = ''.*/cluster_name = 'PGDB_UAT'/" /pgData/pgsql/17.4/dev/postgresql.conf
[postgres@pgdb02 ~]$
[postgres@pgdb02 ~]$ egrep "^(#)?(port|cluster_name)" /pgData/pgsql/17.4/dev/postgresql.conf
port = 5433
cluster_name = 'PGDB_UAT'
[postgres@pgdb02 ~]$

4. Start PostgreSQL Service

[postgres@pgdb02 ~]$ /pgBin/pgsql/17.4/bin/pg_ctl -D /pgData/pgsql/17.4/dev -l logfile start
waiting for server to start.... done
server started
[postgres@pgdb02 ~]$

5. Connect to second instance

[postgres@pgdb02 ~]$ psql -p 5433
psql (17.4)
Type "help" for help.

postgres=# SHOW port;
 port
------
 5433  <-----------
(1 row)

postgres=# SHOW cluster_name;
 cluster_name
--------------
 PGDB_UAT  <---------------
(1 row)

postgres=#\q

[postgres@pgdb02 ~]$ pg_ctl stop -D /pgData/pgsql/17.4/dev
waiting for server to shut down.... done
server stopped
[postgres@pgdb02 ~]$

6. Create second systemd service

[root@pgdb02 ~]# cp /etc/systemd/system/postgresql-17.service /etc/systemd/system/postgresql-17-dev.service
[root@pgdb02 ~]#
[root@pgdb02 ~]# grep -i Environment=PGDATA /etc/systemd/system/postgresql-17-dev.service
Environment=PGDATA=/pgData/pgsql/17.4
[root@pgdb02 ~]#

[root@pgdb02 ~]# sed -i 's|Environment=PGDATA=/pgData/pgsql/17.4|Environment=PGDATA=/pgData/pgsql/17.4/dev|' /etc/systemd/system/postgresql-17-dev.service
[root@pgdb02 ~]# grep -i Environment=PGDATA /etc/systemd/system/postgresql-17-dev.service
Environment=PGDATA=/pgData/pgsql/17.4/dev
[root@pgdb02 ~]#

[root@pgdb02 ~]# systemctl daemon-reload
[root@pgdb02 ~]# systemctl start postgresql-17-dev
[root@pgdb02 ~]# systemctl enable postgresql-17-dev
Created symlink /etc/systemd/system/multi-user.target.wants/postgresql-17-dev.service → /etc/systemd/system/postgresql-17-dev.service.
[root@pgdb02 ~]#
[root@pgdb02 ~]# systemctl status postgresql-17-dev
● postgresql-17-dev.service - PostgreSQL 17 Database Server
     Loaded: loaded (/etc/systemd/system/postgresql-17-dev.service; enabled; preset: disabled)
     Active: active (running) since Sat 2026-06-20 18:25:39 +08; 12s ago
       Docs: https://www.postgresql.org/docs/17/
   Main PID: 4106 (postgres)
      Tasks: 6 (limit: 15700)
     Memory: 15.2M
        CPU: 62ms
     CGroup: /system.slice/postgresql-17-dev.service
             ├─4106 /pgBin/pgsql/17.4/bin/postgres -D /pgData/pgsql/17.4/dev
             ├─4107 "postgres: PGDB_UAT: checkpointer "
             ├─4108 "postgres: PGDB_UAT: background writer "
             ├─4110 "postgres: PGDB_UAT: walwriter "
             ├─4111 "postgres: PGDB_UAT: autovacuum launcher "
             └─4112 "postgres: PGDB_UAT: logical replication launcher "

Jun 20 18:25:39 pgdb02 systemd[1]: Starting PostgreSQL 17 Database Server...
Jun 20 18:25:39 pgdb02 pg_ctl[4103]: waiting for server to start.... done
Jun 20 18:25:39 pgdb02 pg_ctl[4103]: server started
Jun 20 18:25:39 pgdb02 systemd[1]: Started PostgreSQL 17 Database Server.
[root@pgdb02 ~]#

7. Verify instances

[postgres@pgdb02 ~]$ ps -ef | grep postgres
postgres    3711       1  0 17:03 ?        00:00:00 /pgBin/pgsql/17.4/bin/postgres -D /pgData/pgsql/17.4
postgres    3712    3711  0 17:03 ?        00:00:00 postgres: PGDB_SIT: checkpointer
postgres    3713    3711  0 17:03 ?        00:00:00 postgres: PGDB_SIT: background writer
postgres    3715    3711  0 17:03 ?        00:00:00 postgres: PGDB_SIT: walwriter
postgres    3716    3711  0 17:03 ?        00:00:00 postgres: PGDB_SIT: autovacuum launcher
postgres    3717    3711  0 17:03 ?        00:00:00 postgres: PGDB_SIT: logical replication launcher
root        3748    3164  0 17:09 pts/0    00:00:00 su - postgres
postgres    3749    3748  0 17:09 pts/0    00:00:00 -bash
postgres    4106       1  0 18:25 ?        00:00:00 /pgBin/pgsql/17.4/bin/postgres -D /pgData/pgsql/17.4/dev
postgres    4107    4106  0 18:25 ?        00:00:00 postgres: PGDB_UAT: checkpointer
postgres    4108    4106  0 18:25 ?        00:00:00 postgres: PGDB_UAT: background writer
postgres    4110    4106  0 18:25 ?        00:00:00 postgres: PGDB_UAT: walwriter
postgres    4111    4106  0 18:25 ?        00:00:00 postgres: PGDB_UAT: autovacuum launcher
postgres    4112    4106  0 18:25 ?        00:00:00 postgres: PGDB_UAT: logical replication launcher
postgres    4157    3749 99 18:26 pts/0    00:00:00 ps -ef
postgres    4158    3749  0 18:26 pts/0    00:00:00 grep --color=auto postgres
[postgres@pgdb02 ~]$

[postgres@pgdb02 ~]$ ss -tulpn | grep 543
tcp   LISTEN 0      200        127.0.0.1:5433       0.0.0.0:*    users:(("postgres",pid=4106,fd=7))
tcp   LISTEN 0      200        127.0.0.1:5432       0.0.0.0:*    users:(("postgres",pid=3711,fd=7))
tcp   LISTEN 0      200            [::1]:5432          [::]:*    users:(("postgres",pid=3711,fd=6))
tcp   LISTEN 0      200            [::1]:5433          [::]:*    users:(("postgres",pid=4106,fd=6))
[postgres@pgdb02 ~]$

Caution: Your use of any information or materials on this website is entirely at your own risk. It is provided for educational purposes only. It has been tested internally, however, we do not guarantee that it will work for you. Ensure that you run it in your test environment before using.

Thank you,
Rajasekhar Amudala
Email: br8dba@gmail.com
Linkedin: https://www.linkedin.com/in/rajasekhar-amudala/