Tag Archives: PostgreSQL administration

WAL Commit Process

PostgreSQL WAL Commit Process

1. The Modification (In-Memory)

When a user executes a data-modifying query (like INSERT, UPDATE, or DELETE):

  • The change is made to the table or index data inside the Shared Buffers (RAM). The page in memory is now marked as “dirty.”

  • Simultaneously, a record of this exact change is constructed and written sequentially into the WAL Buffers (also in RAM).

2. The COMMIT Command Issued

When the client sends the COMMIT command, PostgreSQL must guarantee that this change will survive a sudden power outage or crash before it can tell the user “Success.”

3. Flushing to Disk (XLogFlush)

To ensure durability without the massive overhead of writing entire data pages to disk immediately, Postgres uses the Write-Ahead Logging protocol:

  • The internal function XLogFlush() is called.

  • It identifies the exact position (Log Sequence Number, or LSN) of the commit record in the WAL Buffer.

  • It issues a synchronous write to flush all WAL buffers up to that LSN out of RAM and into the current 16MB WAL segment file on permanent storage.

  • An fsync() system call is issued to ensure the OS cache actually commits the data to physical disk platters or flash memory.

4. Acknowledgment to the Client

Once the operating system confirms that the WAL record is safely written to the physical storage, the transaction status is updated to “committed” in the commit log (CLOG), and PostgreSQL sends a success acknowledgment back to the client application.

Crucial Architectural Concepts

  • Write-Ahead Rule: The core rule of WAL is that changes to data pages must not be written to permanent database files on disk until the log records describing those changes have been flushed to stable storage. If the server crashes, Postgres reads the WAL from the last checkpoint forward and reapplies the changes (“redoes” them).

  • Asynchronous Commit Alternative: If you set the configuration parameter synchronous_commit = off, Postgres will acknowledge the client’s COMMIT before the WAL buffer is flushed to disk (relying on the WAL Writer background process to flush it within roughly 3 times wal_writer_delay). This massively increases write throughput but introduces a risk of losing up to a split-second of recent transactions if the server suddenly loses power.

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

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/

Uninstall PostgreSQL 17 on Linux (RPM Method)

Uninstall PostgreSQL 17 on Linux (Installed Using RPM Method)

Table of Contents



0. Important Caution Before Proceeding

** Before uninstalling PostgreSQL PostgreSQL 17, first take a logical or physical backup. **

If PostgreSQL was installed using RPM packages, removing the package does not automatically remove:

Database files
WAL files
Backup directories
Custom configuration files

1. Check Installed PostgreSQL RPM Packages

[root@pgdb02 ~]# rpm -qa | grep postgres
postgresql17-libs-17.6-1PGDG.rhel9.x86_64
postgresql17-17.6-1PGDG.rhel9.x86_64
postgresql17-server-17.6-1PGDG.rhel9.x86_64
postgresql17-contrib-17.6-1PGDG.rhel9.x86_64
[root@pgdb02 ~]#

2. Stop PostgreSQL Service

[root@pgdb02 ~]# systemctl stop postgresql-17
[root@pgdb02 ~]# systemctl status postgresql-17
○ postgresql-17.service - PostgreSQL 17 database server
Loaded: loaded (/usr/lib/systemd/system/postgresql-17.service; enabled; preset: disabled)
Active: inactive (dead)
Docs: https://www.postgresql.org/docs/17/static/
[root@pgdb02 ~]#

3. Disable PostgreSQL Service

[root@pgdb02 ~]# systemctl disable postgresql-17
Removed "/etc/systemd/system/multi-user.target.wants/postgresql-17.service".
[root@pgdb02 ~]#

4. Remove and Verify PostgreSQL RPM Packages

WARNING: This permanently deletes all binaries, libraries, and data. Ensure your data is backed up before this step.

[root@pgdb02 ~]# rpm -qa | grep postgres
postgresql17-libs-17.6-1PGDG.rhel9.x86_64
postgresql17-17.6-1PGDG.rhel9.x86_64
postgresql17-server-17.6-1PGDG.rhel9.x86_64
postgresql17-contrib-17.6-1PGDG.rhel9.x86_64
[root@pgdb02 ~]#
[root@pgdb02 ~]# rpm -e postgresql17-contrib-17.6-1PGDG.rhel9.x86_64
[root@pgdb02 ~]# rpm -e postgresql17-server-17.6-1PGDG.rhel9.x86_64
[root@pgdb02 ~]# rpm -e postgresql17-17.6-1PGDG.rhel9.x86_64
[root@pgdb02 ~]# rpm -e postgresql17-libs-17.6-1PGDG.rhel9.x86_64
[root@pgdb02 ~]#

5. Verify Packages Are Removed

[root@pgdb02 ~]# rpm -qa | grep postgres
[root@pgdb02 ~]#

6. Remove PostgreSQL System User (Optional)

[root@pgdb02 ~]# id postgres
uid=26(postgres) gid=26(postgres) groups=26(postgres)
[root@pgdb02 ~]# userdel postgres
[root@pgdb02 ~]#
[root@pgdb02 ~]# groupdel postgres
groupdel: group 'postgres' does not exist
[root@pgdb02 ~]#
[root@pgdb02 ~]# id postgres
id: ‘postgres’: no such user
[root@pgdb02 ~]#

7. Remove PostgreSQL Configuration Files

# It's already removed in step no. 3

[root@pgdb02 ~]# ls -l /usr/lib/systemd/system/postgresql-17.service
ls: cannot access '/usr/lib/systemd/system/postgresql-17.service': No such file or directory
[root@pgdb02 ~]# 
[root@pgdb02 ~]# ls -l /etc/systemd/system/postgresql-17.service
-rw-r--r--. 1 root root 588 Jun 19 21:20 /etc/systemd/system/postgresql-17.service
[root@pgdb02 ~]#
[root@pgdb02 ~]# rm -f /etc/systemd/system/postgresql-17.service
[root@pgdb02 ~]#

8. Verify Complete Removal

[root@pgdb02 ~]# id postgres
id: ‘postgres’: no such user
[root@pgdb02 ~]#
[root@pgdb02 ~]# rpm -qa | grep postgres
[root@pgdb02 ~]#
[root@pgdb02 ~]# systemctl status postgresql-17
Unit postgresql-17.service could not be found.
[root@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/

PostgreSQL

PostgreSQL DBA Step by Step Learning

#PostgreSQL DBA Topics
1How to Install PostgreSQL ON Linux?
2How to Install PostgreSQL on Linux 7 using source code?
3How to START/STOP PostgreSQL ON Linux?
4How to Create Database in PostgreSQL?
5PostgreSQL User Management
6PostgreSQL pg_hba.conf Guide
7PostgreSQL Change Data Directory
8Understanding WAL Files in PostgreSQL – For Oracle DBAs
9Change PostgreSQL WAL Directory Path (pg_wal)
10Enable Archive Mode in PostgreSQL 17
11How to Disable ARCHIVELOG Mode
12PostgreSQL Tablespace Management
13PostgreSQL pg_dump and pg_restore Guide
14PostgreSQL Backup and Restore Using pg_dumpall and psql
15pg_basebackup – Backup, Restore, and Recovery
16Backup & Restore PostgreSQL DB Cluster to Another Host (No Archive Mode)
17Backup & Restore PostgreSQL DB Cluster on Same Host
18Restore PostgreSQL to New Host using pg_basebackup + WAL Archives
19PostgreSQL PITR – Point in Time Recovery
20Configure Streaming Replication in PostgreSQL
21Manual Failover in PostgreSQL Streaming Replication
22Convert Asynchronous Replication to Synchronous Replication

 

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

Backup and Restore on Same Host Using pg_basebackup

How to Backup and Restore PostgreSQL DB Cluster on the Same Host Using pg_basebackup

Table of Contents


1. Environment
2. Verify Existing DB Setup
3. Pre-requisites
4. Take Backup
5. Prepare & Restore
     5.1 Stop PostgreSQL and Clean Directories
     5.2 Remove all from Data & WAL directories
     5.3 Restore Data and WAL
         A. Copy Backup files to $PGDATA
         B. Copy WAL files from $PGDATA/pg_wal to /pgWal/pgsql17/wal/
         C. Remove the existing $PGDATA/pg_wal directory
         D. Create a symbolic link pointing $PGDATA/pg_wal to a separate WAL directory
         E. Set Permissions
6. Start PostgreSQL
7. Final Verification


1. Environment

ASPECTEnv
Hostnamelxicbpgdsgv01
IP Address192.168.2.51
OSRHEL 9
DB VersionPostgreSQL v17.6
Archive modearchive_mode=off
pgData/pgData/pgsql17/data
WAL Directory/pgWal/pgsql17/wal
Tablespacepg_default
DatabasesDELL, ORCL

2. Verify Existing DB Setup

[postgres@lxicbpgdsgv01 ~]$ psql
psql (17.6)
Type "help" for help.

postgres=# \l+
                                                                                       List of databases
   Name    |  Owner   | Encoding | Locale Provider |   Collate   |    Ctype    | Locale | ICU Rules |   Access privileges   |  Size   | Tablespace |                Description
-----------+----------+----------+-----------------+-------------+-------------+--------+-----------+-----------------------+---------+------------+--------------------------------------------
 dell      | postgres | UTF8     | libc            | en_SG.UTF-8 | en_SG.UTF-8 |        |           |                       | 7763 kB | pg_default |
 orcl      | postgres | UTF8     | libc            | en_SG.UTF-8 | en_SG.UTF-8 |        |           |                       | 7907 kB | pg_default |
 postgres  | postgres | UTF8     | libc            | en_SG.UTF-8 | en_SG.UTF-8 |        |           |                       | 492 MB  | pg_default | default administrative connection database
 template0 | postgres | UTF8     | libc            | en_SG.UTF-8 | en_SG.UTF-8 |        |           | =c/postgres          +| 7545 kB | pg_default | unmodifiable empty database
           |          |          |                 |             |             |        |           | postgres=CTc/postgres |         |            |
 template1 | postgres | UTF8     | libc            | en_SG.UTF-8 | en_SG.UTF-8 |        |           | =c/postgres          +| 7723 kB | pg_default | default template for new databases
           |          |          |                 |             |             |        |           | postgres=CTc/postgres |         |            |
(5 rows)

postgres=# \db
       List of tablespaces
    Name    |  Owner   | Location
------------+----------+----------
 pg_default | postgres |
 pg_global  | postgres |
(2 rows)

postgres=# \c dell
You are now connected to database "dell" as user "postgres".
dell=# select * from test.emp;
 name | designation | project | company
------+-------------+---------+---------
 Sugi | DBA         | Jetstar | iGATE
 Teja | DBA         | RCM     | iGATE
 RAJ  | DBA         | RCM     | iGATE
(3 rows)

dell=#

3. Pre-requisites

  • Verify postgresql.conf
postgres=# SHOW wal_level;
 wal_level
-----------
 replica <----
(1 row)

postgres=#
postgres=# SHOW max_wal_senders;
 max_wal_senders
-----------------
 10
(1 row)

postgres=# SHOW archive_mode;
 archive_mode
--------------
 off
(1 row)

postgres=# 
  • Verify pg_hba.conf
# TYPE  DATABASE        USER            ADDRESS             METHOD
# Local connections for replication (for pg_basebackup run locally)
local   replication     all                                 trust

# Remote connections for replication (for pg_basebackup run remotely)
#host    replication     repl_user       192.168.2.52/32     scram-sha-256

  • Verify user permissions:REPLICATION or SUPERUSER required
postgres=# \du
                             List of roles
 Role name |                         Attributes
-----------+------------------------------------------------------------
 postgres  | Superuser, Create role, Create DB, Replication, Bypass RLS

postgres=#
  • Verify free space for backup
[postgres@lxicbpgdsgv01 ~]$ du -sh /pgData/pgsql17/data/
524M    /pgData/pgsql17/data/
[postgres@lxicbpgdsgv01 ~]$
[postgres@lxicbpgdsgv01 ~]$ du -sh /pgWal/pgsql17/wal/
801M    /pgWal/pgsql17/wal/
[postgres@lxicbpgdsgv01 ~]$

[postgres@lxicbpgdsgv01 ~]$ df -h /pgBackup/
Filesystem      Size  Used Avail Use% Mounted on
/dev/sdd1       100G  746M  100G   1% /pgBackup <----
[postgres@lxicbpgdsgv01 ~]$ mkdir -p /pgBackup/pgsql17/backup/basebackup_10OCT2025
[postgres@lxicbpgdsgv01 ~]$
[postgres@lxicbpgdsgv01 ~]$ mkdir -p /pgBackup/pgsql17/backup/log/
[postgres@lxicbpgdsgv01 ~]$

4. Take Backup

[postgres@lxicbpgdsgv01 ~]$ ls -ltrh /pgWal/pgsql17/wal | wc -l
53 <---- 
[postgres@lxicbpgdsgv01 ~]$

pg_basebackup does not include all files from the pg_wal directory in the backup. Instead, it selectively includes only the WAL files required to make the base backup consistent at the point in time the backup was taken.

-- If you want to store the base backup and WAL files in separate backup directories. 

nohup pg_basebackup -U postgres -D /pgBackup/pgsql17/backup/basebackup_10OCT2025 --waldir=/pgBackup/pgsql17/backup/wal_backup -Fp -Xs -P -v > /pgBackup/pgsql17/backup/log/basebackup_10OCT2025.log 2>&1 &

The --waldir option in pg_basebackup is supported only when using the plain format (-Fp), not with the tar format (-Ft).

If we want symlinks preserved → use (both -Fp & --waldir use together) -Fp --waldir=/pgWal/pgsql17/wal

-- OR --

The directory mush be empty: /pgBackup/pgsql17/backup/basebackup_10OCT2025

[postgres@lxicbpgdsgv01 ~]$ nohup pg_basebackup -U postgres -D /pgBackup/pgsql17/backup/basebackup_10OCT2025 -Fp -Xs -P -v > /pgBackup/pgsql17/backup/log/basebackup_10OCT2025.log 2>&1 &
[1] 4973
[postgres@lxicbpgdsgv01 ~]$

[postgres@lxicbpgdsgv01 ~]$ cat /pgBackup/pgsql17/backup/log/basebackup_10OCT2025.log
nohup: ignoring input
pg_basebackup: initiating base backup, waiting for checkpoint to complete
pg_basebackup: checkpoint completed
pg_basebackup: write-ahead log start point: 0/85000028 on timeline 1
pg_basebackup: starting background WAL receiver
pg_basebackup: created temporary replication slot "pg_basebackup_4975"
279413/536037 kB (52%), 0/1 tablespace (...asebackup_10OCT2025/base/5/16533)
536047/536047 kB (100%), 0/1 tablespace (...ckup_10OCT2025/global/pg_control)
536047/536047 kB (100%), 1/1 tablespace
pg_basebackup: write-ahead log end point: 0/85000158
pg_basebackup: waiting for background process to finish streaming ...
pg_basebackup: syncing data to disk ...
pg_basebackup: renaming backup_manifest.tmp to backup_manifest
pg_basebackup: base backup completed  <-----
[postgres@lxicbpgdsgv01 ~]$

5. Prepare & Restore

5.1 Stop PostgreSQL and Clean Directories

[root@lxicbpgdsgv01 ~]# systemctl stop postgresql-17.service
[root@lxicbpgdsgv01 ~]# 
[root@lxicbpgdsgv01 ~]# ps -ef | grep postgres
root        5057    3151  0 18:57 pts/0    00:00:00 grep --color=auto postgres
[root@lxicbpgdsgv01 ~]#

5.2 Remove all from Data & WAL directories

-- Remove all from PGDATA directory

[root@lxicbpgdsgv01 ~]# rm -rf /pgData/pgsql17/data/*
[root@lxicbpgdsgv01 ~]# ls -ltr /pgData/pgsql17/data/
total 0
[root@lxicbpgdsgv01 ~]#

-- Remove all from WAL directory 

[root@lxicbpgdsgv01 ~]# rm -rf /pgWal/pgsql17/wal/*
[root@lxicbpgdsgv01 ~]# ls -ltr /pgWal/pgsql17/wal/
total 0
[root@lxicbpgdsgv01 ~]#

5.3 Restore Data and WAL

A. Copy Backup files to $PGDATA
Since we did not use the -Fp format with the --waldir option, all required WAL files will be included in the backup under the default path: PGDATA/pg_wal.

[postgres@lxicbpgdsgv01 ~]$ ls -ltr /pgData/pgsql17/data/
total 0
[postgres@lxicbpgdsgv01 ~]$ cd /pgBackup/pgsql17/backup/basebackup_10OCT2025/
[postgres@lxicbpgdsgv01 basebackup_10OCT2025]$ cp -Rp * /pgData/pgsql17/data/
[postgres@lxicbpgdsgv01 basebackup_10OCT2025]$
[postgres@lxicbpgdsgv01 basebackup_10OCT2025]$ ls -ltr /pgData/pgsql17/data/
total 296
-rw-------. 1 postgres postgres    227 Oct 10 18:41 backup_label
drwx------. 4 postgres postgres     77 Oct 10 18:41 pg_wal
drwx------. 7 postgres postgres     59 Oct 10 18:41 base
drwx------. 4 postgres postgres     68 Oct 10 18:41 pg_logical
drwx------. 2 postgres postgres      6 Oct 10 18:41 pg_dynshmem
drwx------. 2 postgres postgres      6 Oct 10 18:41 pg_commit_ts
drwx------. 2 postgres postgres    110 Oct 10 18:41 log
-rw-------. 1 postgres postgres   1169 Oct 10 18:41 postgresql.conf.bkp_10sep2025
-rw-------. 1 postgres postgres  30702 Oct 10 18:41 postgresql.conf.bkp
-rw-------. 1 postgres postgres     88 Oct 10 18:41 postgresql.auto.conf
drwx------. 2 postgres postgres     18 Oct 10 18:41 pg_xact
-rw-------. 1 postgres postgres      3 Oct 10 18:41 PG_VERSION
drwx------. 2 postgres postgres      6 Oct 10 18:41 pg_twophase
drwx------. 2 postgres postgres      6 Oct 10 18:41 pg_tblspc
drwx------. 2 postgres postgres      6 Oct 10 18:41 pg_subtrans
drwx------. 2 postgres postgres      6 Oct 10 18:41 pg_stat_tmp
drwx------. 2 postgres postgres      6 Oct 10 18:41 pg_stat
drwx------. 2 postgres postgres      6 Oct 10 18:41 pg_snapshots
drwx------. 2 postgres postgres      6 Oct 10 18:41 pg_serial
drwx------. 2 postgres postgres      6 Oct 10 18:41 pg_replslot
drwx------. 2 postgres postgres      6 Oct 10 18:41 pg_notify
drwx------. 4 postgres postgres     36 Oct 10 18:41 pg_multixact
-rw-------. 1 postgres postgres   2640 Oct 10 18:41 pg_ident.conf
-rw-------. 1 postgres postgres   5600 Oct 10 18:41 pg_hba.conf
-rw-------. 1 postgres postgres   1171 Oct 10 18:41 postgresql.conf
drwx------. 2 postgres postgres   4096 Oct 10 18:41 global
-rw-------. 1 postgres postgres     30 Oct 10 18:41 current_logfiles
-rw-------. 1 postgres postgres 227736 Oct 10 18:41 backup_manifest
[postgres@lxicbpgdsgv01 basebackup_10OCT2025]$
B. Copy WAL files from $PGDATA/pg_wal to /pgWal/pgsql17/wal/
[postgres@lxicbpgdsgv01 ~]$ ls -ltr /pgWal/pgsql17/wal/
total 0
[postgres@lxicbpgdsgv01 ~]$
[postgres@lxicbpgdsgv01 ~]$ cd /pgData/pgsql17/data/pg_wal/
[postgres@lxicbpgdsgv01 pg_wal]$ cp -Rp * /pgWal/pgsql17/wal
[postgres@lxicbpgdsgv01 pg_wal]$
[postgres@lxicbpgdsgv01 pg_wal]$ ls -ltr /pgWal/pgsql17/wal
total 16384
drwx------. 2 postgres postgres        6 Oct 10 18:41 summaries
drwx------. 2 postgres postgres        6 Oct 10 18:41 archive_status
-rw-------. 1 postgres postgres 16777216 Oct 10 18:41 000000010000000000000085
[postgres@lxicbpgdsgv01 pg_wal]$ cd
[postgres@lxicbpgdsgv01 ~]$
C. Remove the existing $PGDATA/pg_wal directory
[postgres@lxicbpgdsgv01 ~]$ rm -rf /pgData/pgsql17/data/pg_wal
[postgres@lxicbpgdsgv01 ~]$
D. Create a symbolic link pointing $PGDATA/pg_wal to a separate WAL directory
[postgres@lxicbpgdsgv01 ~]$ ln -s /pgWal/pgsql17/wal /pgData/pgsql17/data/pg_wal
[postgres@lxicbpgdsgv01 ~]$
[postgres@lxicbpgdsgv01 ~]$ ls -ld /pgData/pgsql17/data/pg_wal
lrwxrwxrwx. 1 postgres postgres 18 Oct 10 19:43 /pgData/pgsql17/data/pg_wal -> /pgWal/pgsql17/wal
[postgres@lxicbpgdsgv01 ~]$
E. Set Permissions
[postgres@lxicbpgdsgv01 ~]$ chown -R postgres:postgres /pgData/pgsql17/data
[postgres@lxicbpgdsgv01 ~]$ chmod 700 /pgData/pgsql17/data
[postgres@lxicbpgdsgv01 ~]$ chown -R postgres:postgres /pgWal/pgsql17/wal
[postgres@lxicbpgdsgv01 ~]$ chmod 700 /pgWal/pgsql17/wal

6. Start PostgreSQL

[root@lxicbpgdsgv01 ~]# systemctl start postgresql-17.service
[root@lxicbpgdsgv01 ~]# systemctl status postgresql-17.service
● postgresql-17.service - PostgreSQL 17 database server
     Loaded: loaded (/usr/lib/systemd/system/postgresql-17.service; enabled; preset: disabled)
     Active: active (running) since Fri 2025-10-10 19:45:21 +08; 5s ago
       Docs: https://www.postgresql.org/docs/17/static/
    Process: 5230 ExecStartPre=/usr/pgsql-17/bin/postgresql-17-check-db-dir ${PGDATA} (code=exited, status=0/SUCCESS)
   Main PID: 5235 (postgres)
      Tasks: 7 (limit: 15835)
     Memory: 34.2M
        CPU: 94ms
     CGroup: /system.slice/postgresql-17.service
             ├─5235 /usr/pgsql-17/bin/postgres -D /pgData/pgsql17/data/
             ├─5236 "postgres: logger "
             ├─5237 "postgres: checkpointer "
             ├─5238 "postgres: background writer "
             ├─5240 "postgres: walwriter "
             ├─5241 "postgres: autovacuum launcher "
             └─5242 "postgres: logical replication launcher "

Oct 10 19:45:21 lxicbpgdsgv01.rajasekhar.com systemd[1]: Starting PostgreSQL 17 database server...
Oct 10 19:45:21 lxicbpgdsgv01.rajasekhar.com postgres[5235]: 2025-10-10 19:45:21.177 +08 [5235] LOG:  redirecting log output to logging collector process
Oct 10 19:45:21 lxicbpgdsgv01.rajasekhar.com postgres[5235]: 2025-10-10 19:45:21.177 +08 [5235] HINT:  Future log output will appear in directory "log".
Oct 10 19:45:21 lxicbpgdsgv01.rajasekhar.com systemd[1]: Started PostgreSQL 17 database server.
[root@lxicbpgdsgv01 ~]#

7. Final Verification

[postgres@lxicbpgdsgv01 ~]$ psql
psql (17.6)
Type "help" for help.

postgres=# \l+
                                                                                       List of databases
   Name    |  Owner   | Encoding | Locale Provider |   Collate   |    Ctype    | Locale | ICU Rules |   Access privileges   |  Size   | Tablespace |                Description
-----------+----------+----------+-----------------+-------------+-------------+--------+-----------+-----------------------+---------+------------+--------------------------------------------
 dell      | postgres | UTF8     | libc            | en_SG.UTF-8 | en_SG.UTF-8 |        |           |                       | 7609 kB | pg_default |
 orcl      | postgres | UTF8     | libc            | en_SG.UTF-8 | en_SG.UTF-8 |        |           |                       | 7753 kB | pg_default |
 postgres  | postgres | UTF8     | libc            | en_SG.UTF-8 | en_SG.UTF-8 |        |           |                       | 492 MB  | pg_default | default administrative connection database
 template0 | postgres | UTF8     | libc            | en_SG.UTF-8 | en_SG.UTF-8 |        |           | =c/postgres          +| 7545 kB | pg_default | unmodifiable empty database
           |          |          |                 |             |             |        |           | postgres=CTc/postgres |         |            |
 template1 | postgres | UTF8     | libc            | en_SG.UTF-8 | en_SG.UTF-8 |        |           | =c/postgres          +| 7569 kB | pg_default | default template for new databases
           |          |          |                 |             |             |        |           | postgres=CTc/postgres |         |            |
(5 rows)

postgres=# \db
       List of tablespaces
    Name    |  Owner   | Location
------------+----------+----------
 pg_default | postgres |
 pg_global  | postgres |
(2 rows)

postgres=# \c dell
You are now connected to database "dell" as user "postgres".
dell=# select * from test.emp;
 name | designation | project | company
------+-------------+---------+---------
 Sugi | DBA         | Jetstar | iGATE
 Teja | DBA         | RCM     | iGATE
 RAJ  | DBA         | RCM     | iGATE
(3 rows)

dell=#

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/

Disable ARCHIVELOG Mode

How to Disable ARCHIVELOG Mode

Table of Contents


1. Verify Existing Archive Mode
2. Edit the archive settings
3. Restart PostgreSQL
4. Verify Current Mode
5. Verify WAL Archiving Behavior


1. Verify Existing Archive Mode

postgres=# SHOW archive_mode;
 archive_mode
--------------
 on  <------ 
(1 row)

postgres=#

postgres=# SHOW archive_command;
        archive_command
-------------------------------
 cp %p /pgArch/pgsql17/arch/%f  <----- 
(1 row)

postgres=#

2. Edit the archive settings


[postgres@lxicbpgdsgv01 ~]$ cp /pgData/pgsql17/data/postgresql.conf /pgData/pgsql17/data/postgresql.conf.bkp_10sep2025
[postgres@lxicbpgdsgv01 ~]$ vi /pgData/pgsql17/data/postgresql.conf

#archive_mode = on
#archive_command = 'cp %p /pgArch/pgsql17/arch/%f'

3. Restart PostgreSQL

[root@lxicbpgdsgv01 ~]# systemctl stop postgresql-17.service
[root@lxicbpgdsgv01 ~]#
[root@lxicbpgdsgv01 ~]# systemctl start  postgresql-17.service
[root@lxicbpgdsgv01 ~]#
[root@lxicbpgdsgv01 ~]# systemctl status postgresql-17.service
● postgresql-17.service - PostgreSQL 17 database server
     Loaded: loaded (/usr/lib/systemd/system/postgresql-17.service; enabled; preset: disabled)
     Active: active (running) since Thu 2025-10-09 16:34:01 +08; 3s ago
       Docs: https://www.postgresql.org/docs/17/static/
    Process: 3492 ExecStartPre=/usr/pgsql-17/bin/postgresql-17-check-db-dir ${PGDATA} (code=exited, status=0/SUCCESS)
   Main PID: 3497 (postgres)
      Tasks: 7 (limit: 15835)
     Memory: 17.6M
        CPU: 92ms
     CGroup: /system.slice/postgresql-17.service
             ├─3497 /usr/pgsql-17/bin/postgres -D /pgData/pgsql17/data/
             ├─3498 "postgres: logger "
             ├─3499 "postgres: checkpointer "
             ├─3500 "postgres: background writer "
             ├─3502 "postgres: walwriter "
             ├─3503 "postgres: autovacuum launcher "
             └─3504 "postgres: logical replication launcher "

Oct 09 16:34:01 lxicbpgdsgv01.rajasekhar.com systemd[1]: Starting PostgreSQL 17 database server...
Oct 09 16:34:01 lxicbpgdsgv01.rajasekhar.com postgres[3497]: 2025-10-09 16:34:01.929 +08 [3497] LOG:  redirecting log output to logging collector process
Oct 09 16:34:01 lxicbpgdsgv01.rajasekhar.com postgres[3497]: 2025-10-09 16:34:01.929 +08 [3497] HINT:  Future log output will appear in directory "log".
Oct 09 16:34:01 lxicbpgdsgv01.rajasekhar.com systemd[1]: Started PostgreSQL 17 database server.
[root@lxicbpgdsgv01 ~]#

4. Verify Current Mode

[postgres@lxicbpgdsgv01 ~]$ psql
psql (17.6)
Type "help" for help.

postgres=# SHOW archive_mode;
 archive_mode
--------------
 off  <------ it's disabled
(1 row)

postgres=# SHOW archive_command;
 archive_command
-----------------
 (disabled) <-------
(1 row)

postgres=#

5. Verify WAL Archiving Behavior


postgres=# CHECKPOINT;
CHECKPOINT
postgres=#
postgres=# CHECKPOINT;
CHECKPOINT
postgres=# CHECKPOINT;
CHECKPOINT
postgres=#
postgres=# exit
postgres=# SELECT pg_switch_wal();
 pg_switch_wal
---------------
 0/44000000
(1 row)

postgres=# SELECT pg_switch_wal();
 pg_switch_wal
---------------
 0/44000000
(1 row)

postgres=# SELECT pg_switch_wal();
 pg_switch_wal
---------------
 0/44000000
(1 row)

postgres=#
[postgres@lxicbpgdsgv01 ~]$ ls -ltr /pgArch/pgsql17/arch/
total 0  <---- Archivelogs not generating
[postgres@lxicbpgdsgv01 ~]$

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/

Change PostgreSQL WAL Directory Path (pg_wal)

Change WAL Directory Path (pg_wal) in PostgreSQL

Table of Contents


0. Aim
1. Verify Existing pg_wal Directory
2. Create the New Directory
3. Stop PostgreSQL Service
4. Copy WAL Files to New Location
5. Backup Old WAL Directory
6. Create Symlink
7. Fix Permissions
8. Start PostgreSQL Service
9. Verify WAL Functionality
10. Remove Old WAL Directory (Optional)


0. Aim

To change the PostgreSQL 17 WAL File directory from its default location to new mount point

From : /pgData/pgsql17/data/pg_wal

TO : /pgWal/pgsql17/wal

1. Verify Existing pg_wal directory


[postgres@lxicbpgdsgv01 ~]$ psql
psql (17.6)
Type "help" for help.

postgres=# SELECT current_setting('data_directory') || '/pg_wal' AS wal_directory;
        wal_directory
-----------------------------
 /pgData/pgsql17/data/pg_wal  <----- 
(1 row)

postgres=# exit
[postgres@lxicbpgdsgv01 ~]$ ls -lrth /pgData/pgsql17/data/pg_wal
total 48M
drwx------. 2 postgres postgres   6 Sep 30 21:50 summaries
-rw-------. 1 postgres postgres 16M Oct  8 04:24 000000010000000000000008
-rw-------. 1 postgres postgres 16M Oct  8 16:08 000000010000000000000006
-rw-------. 1 postgres postgres 16M Oct  8 16:08 000000010000000000000007
drwx------. 2 postgres postgres  43 Oct  8 16:08 archive_status
[postgres@lxicbpgdsgv01 ~]$

[postgres@lxicbpgdsgv01 ~]$ du -sh /pgData/pgsql17/data/pg_wal
48M     /pgData/pgsql17/data/pg_wal
[postgres@lxicbpgdsgv01 ~]$

2. Create the New Directory on a new disk

[root@lxicbpgdsgv01 ~]# mkdir -p /pgWal/pgsql17/wal
[root@lxicbpgdsgv01 ~]# chown postgres:postgres /pgWal/pgsql17/wal
[root@lxicbpgdsgv01 ~]# chmod 700 /pgWal/pgsql17/wal
[root@lxicbpgdsgv01 ~]#

3. Stop PostgreSQL Service

[root@lxicbpgdsgv01 ~]# systemctl stop postgresql-17.service
[root@lxicbpgdsgv01 ~]#
[root@lxicbpgdsgv01 ~]# ps -ef | grep postgres
root        6887    6721  0 16:08 pts/0    00:00:00 grep --color=auto postgres
[root@lxicbpgdsgv01 ~]#

4. Copy Existing WAL Files to New Location

[postgres@lxicbpgdsgv01 ~]$ nohup rsync -avh --progress /pgData/pgsql17/data/pg_wal/ /pgWal/pgsql17/wal/ > rsync_pgwal.log 2>&1 &
[1] 6943
[postgres@lxicbpgdsgv01 ~]$
[postgres@lxicbpgdsgv01 ~]$
[1]+  Done                    nohup rsync -avh --progress /pgData/pgsql17/data/pg_wal/ /pgWal/pgsql17/wal/ > rsync_pgwal.log 2>&1
[postgres@lxicbpgdsgv01 ~]$

[postgres@lxicbpgdsgv01 ~]$ cat rsync_pgwal.log
nohup: ignoring input
sending incremental file list
./
000000010000000000000006
         16.78M 100%   81.89MB/s    0:00:00 (xfr#1, to-chk=5/7)
000000010000000000000007
         16.78M 100%   43.84MB/s    0:00:00 (xfr#2, to-chk=4/7)
000000010000000000000008
         16.78M 100%   31.07MB/s    0:00:00 (xfr#3, to-chk=3/7)
archive_status/
archive_status/000000010000000000000006.done
              0 100%    0.00kB/s    0:00:00 (xfr#4, to-chk=0/7)
summaries/

sent 50.34M bytes  received 107 bytes  33.56M bytes/sec
total size is 50.33M  speedup is 1.00
[postgres@lxicbpgdsgv01 ~]$

[postgres@lxicbpgdsgv01 ~]$ ls -lrth /pgWal/pgsql17/wal/
total 48M
drwx------. 2 postgres postgres   6 Sep 30 21:50 summaries
-rw-------. 1 postgres postgres 16M Oct  8 04:24 000000010000000000000008
-rw-------. 1 postgres postgres 16M Oct  8 16:08 000000010000000000000006
-rw-------. 1 postgres postgres 16M Oct  8 16:08 000000010000000000000007
drwx------. 2 postgres postgres  43 Oct  8 16:08 archive_status
[postgres@lxicbpgdsgv01 ~]$

[postgres@lxicbpgdsgv01 ~]$ du -sh /pgWal/pgsql17/wal/
48M     /pgWal/pgsql17/wal/
[postgres@lxicbpgdsgv01 ~]$

5. Move old directory as backup

[postgres@lxicbpgdsgv01 ~]$ mv /pgData/pgsql17/data/pg_wal /pgData/pgsql17/data/pg_wal.bak
[postgres@lxicbpgdsgv01 ~]$

[postgres@lxicbpgdsgv01 ~]$ ls -ld /pgData/pgsql17/data/pg_wal
ls: cannot access '/pgData/pgsql17/data/pg_wal': No such file or directory
[postgres@lxicbpgdsgv01 ~]$

[postgres@lxicbpgdsgv01 ~]$ ls -ld /pgData/pgsql17/data/pg_wal.bak
drwx------. 4 postgres postgres 141 Oct  8 16:08 /pgData/pgsql17/data/pg_wal.bak
[postgres@lxicbpgdsgv01 ~]$

6. Create symlink

[postgres@lxicbpgdsgv01 ~]$ ln -s /pgWal/pgsql17/wal /pgData/pgsql17/data/pg_wal
[postgres@lxicbpgdsgv01 ~]$
[postgres@lxicbpgdsgv01 ~]$ ls -ltr /pgData/pgsql17/data/pg_wal
lrwxrwxrwx. 1 postgres postgres 18 Oct  8 16:16 /pgData/pgsql17/data/pg_wal -> /pgWal/pgsql17/wal
[postgres@lxicbpgdsgv01 ~]$

7. Fix permissions (if required)

[postgres@lxicbpgdsgv01 ~]$ chown -R postgres:postgres /pgWal/pgsql17/wal

8. Start PostgreSQL Service

[root@lxicbpgdsgv01 ~]# systemctl start postgresql-17.service
[root@lxicbpgdsgv01 ~]#
[root@lxicbpgdsgv01 ~]# systemctl status postgresql-17.service
● postgresql-17.service - PostgreSQL 17 database server
     Loaded: loaded (/usr/lib/systemd/system/postgresql-17.service; enabled; preset: disabled)
     Active: active (running) since Wed 2025-10-08 16:20:46 +08; 7s ago
       Docs: https://www.postgresql.org/docs/17/static/
    Process: 7079 ExecStartPre=/usr/pgsql-17/bin/postgresql-17-check-db-dir ${PGDATA} (code=exited, status=0/SUCCESS)
   Main PID: 7084 (postgres)
      Tasks: 8 (limit: 15835)
     Memory: 18.1M
        CPU: 94ms
     CGroup: /system.slice/postgresql-17.service
             ├─7084 /usr/pgsql-17/bin/postgres -D /pgData/pgsql17/data/
             ├─7086 "postgres: logger "
             ├─7087 "postgres: checkpointer "
             ├─7088 "postgres: background writer "
             ├─7090 "postgres: walwriter "
             ├─7091 "postgres: autovacuum launcher "
             ├─7092 "postgres: archiver "
             └─7093 "postgres: logical replication launcher "

Oct 08 16:20:46 lxicbpgdsgv01.rajasekhar.com systemd[1]: Starting PostgreSQL 17 database server...
Oct 08 16:20:46 lxicbpgdsgv01.rajasekhar.com postgres[7084]: 2025-10-08 16:20:46.162 +08 [7084] LOG:  redirecting log output to logging collector process
Oct 08 16:20:46 lxicbpgdsgv01.rajasekhar.com postgres[7084]: 2025-10-08 16:20:46.162 +08 [7084] HINT:  Future log output will appear in directory "log".
Oct 08 16:20:46 lxicbpgdsgv01.rajasekhar.com systemd[1]: Started PostgreSQL 17 database server.
[root@lxicbpgdsgv01 ~]#

9. Verify

-- Load WAL File generation (Testing)

postgres=# -- Create test table
DROP TABLE IF EXISTS wal_test;
CREATE TABLE wal_test (
    id serial PRIMARY KEY,
    data text
);

-- Generate WAL traffic
DO $$
DECLARE
    i integer;
BEGIN
    FOR i IN 1..50 LOOP
        -- INSERT: 10,000 rows
        INSERT INTO wal_test (data)
        SELECT repeat('wal_test_data_', 50)
        FROM generate_series(1, 10000);

        -- UPDATE: 5,000 rows using CTE with LIMIT
        WITH to_update AS (
            SELECT id FROM wal_test WHERE id % 2 = 0 LIMIT 5000
        )
        UPDATE wal_test
        SET data = data || '_updated'
        WHERE id IN (SELECT id FROM to_update);

        -- DELETE: 5,000 rows using CTE with LIMIT
        WITH to_delete AS (
            SELECT id FROM wal_test WHERE id % 3 = 0 LIMIT 5000
        )
        DELETE FROM wal_test
        WHERE id IN (SELECT id FROM to_delete);

        -- Commit to flush WAL
        COMMIT;

        -- Optional pause to slow down the loop
        PERFORM pg_sleep(0.5);
    END LOOP;
END$$;
DROP TABLE
CREATE TABLE
DO
postgres=# exit
[postgres@lxicbpgdsgv01 ~]$
[postgres@lxicbpgdsgv01 ~]$ ls -lrth  /pgWal/pgsql17/wal
total 752M
drwx------. 2 postgres postgres    6 Sep 30 21:50 summaries
-rw-------. 1 postgres postgres  16M Oct  8 16:34 000000010000000000000009
-rw-------. 1 postgres postgres  16M Oct  8 16:34 00000001000000000000000A
-rw-------. 1 postgres postgres  16M Oct  8 16:34 00000001000000000000000B
-rw-------. 1 postgres postgres  16M Oct  8 16:34 00000001000000000000000C
-rw-------. 1 postgres postgres  16M Oct  8 16:34 00000001000000000000000D
-rw-------. 1 postgres postgres  16M Oct  8 16:34 00000001000000000000000E
-rw-------. 1 postgres postgres  16M Oct  8 16:34 00000001000000000000000F
-rw-------. 1 postgres postgres  16M Oct  8 16:34 000000010000000000000010
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000011
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000012
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000013
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000014
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000015
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000016
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000017
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000018
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000019
-rw-------. 1 postgres postgres  16M Oct  8 16:35 00000001000000000000001A
-rw-------. 1 postgres postgres  16M Oct  8 16:35 00000001000000000000001B
-rw-------. 1 postgres postgres  16M Oct  8 16:35 00000001000000000000001C
-rw-------. 1 postgres postgres  16M Oct  8 16:35 00000001000000000000001D
-rw-------. 1 postgres postgres  16M Oct  8 16:35 00000001000000000000001E
-rw-------. 1 postgres postgres  16M Oct  8 16:35 00000001000000000000001F
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000020
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000021
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000022
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000023
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000024
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000025
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000026
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000027
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000028
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000029
-rw-------. 1 postgres postgres  16M Oct  8 16:35 00000001000000000000002A
-rw-------. 1 postgres postgres  16M Oct  8 16:35 00000001000000000000002B
-rw-------. 1 postgres postgres  16M Oct  8 16:35 00000001000000000000002C
-rw-------. 1 postgres postgres  16M Oct  8 16:35 00000001000000000000002D
-rw-------. 1 postgres postgres  16M Oct  8 16:35 00000001000000000000002E
-rw-------. 1 postgres postgres  16M Oct  8 16:35 00000001000000000000002F
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000030
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000031
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000032
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000033
-rw-------. 1 postgres postgres  16M Oct  8 16:35 000000010000000000000034
-rw-------. 1 postgres postgres  16M Oct  8 16:36 000000010000000000000035
drwx------. 2 postgres postgres 4.0K Oct  8 16:36 archive_status
-rw-------. 1 postgres postgres  16M Oct  8 16:36 xlogtemp.7289
[postgres@lxicbpgdsgv01 ~]$

10. Remove Old WAL Directory (Optional, later)

[postgres@lxicbpgdsgv01 ~]$ ls -ld /pgData/pgsql17/data/pg_wal.bak
drwx------. 4 postgres postgres 141 Oct  8 16:08 /pgData/pgsql17/data/pg_wal.bak
[postgres@lxicbpgdsgv01 ~]$ rm -rf /pgData/pgsql17/data/pg_wal.bak
[postgres@lxicbpgdsgv01 ~]$
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

PostgreSQL Backup and Restore Using pg_dumpall

PostgreSQL Backup and Restore Using pg_dumpall and psql

Table of Contents


0. Introduction

Backup:

1. Backup All Databases
2. Backup Users/Roles Definition
3. Backup Tablespaces Definition
4. Backup Schema Only (No Data)
5. Backup Data Only (No Schema)
6. Backup Data as INSERT Commands
7. Backup Global Objects Only (No Databases)

Restore:

8. Restore on Same Host

9. Restore to Another Host (Different Tablespace Paths)


Click to expand pg_dumpall –help
[postgres@lxtrdpgdsgv01 ~]$ pg_dumpall --help
pg_dumpall extracts a PostgreSQL database cluster into an SQL script file.

Usage:
  pg_dumpall [OPTION]...

General options:
  -f, --file=FILENAME          output file name
  -v, --verbose                verbose mode
  -V, --version                output version information, then exit
  --lock-wait-timeout=TIMEOUT  fail after waiting TIMEOUT for a table lock
  -?, --help                   show this help, then exit

Options controlling the output content:
  -a, --data-only              dump only the data, not the schema
  -c, --clean                  clean (drop) databases before recreating
  -E, --encoding=ENCODING      dump the data in encoding ENCODING
  -g, --globals-only           dump only global objects, no databases
  -O, --no-owner               skip restoration of object ownership
  -r, --roles-only             dump only roles, no databases or tablespaces
  -s, --schema-only            dump only the schema, no data
  -S, --superuser=NAME         superuser user name to use in the dump
  -t, --tablespaces-only       dump only tablespaces, no databases or roles
  -x, --no-privileges          do not dump privileges (grant/revoke)
  --binary-upgrade             for use by upgrade utilities only
  --column-inserts             dump data as INSERT commands with column names
  --disable-dollar-quoting     disable dollar quoting, use SQL standard quoting
  --disable-triggers           disable triggers during data-only restore
  --exclude-database=PATTERN   exclude databases whose name matches PATTERN
  --extra-float-digits=NUM     override default setting for extra_float_digits
  --if-exists                  use IF EXISTS when dropping objects
  --inserts                    dump data as INSERT commands, rather than COPY
  --load-via-partition-root    load partitions via the root table
  --no-comments                do not dump comments
  --no-publications            do not dump publications
  --no-role-passwords          do not dump passwords for roles
  --no-security-labels         do not dump security label assignments
  --no-subscriptions           do not dump subscriptions
  --no-sync                    do not wait for changes to be written safely to disk
  --no-table-access-method     do not dump table access methods
  --no-tablespaces             do not dump tablespace assignments
  --no-toast-compression       do not dump TOAST compression methods
  --no-unlogged-table-data     do not dump unlogged table data
  --on-conflict-do-nothing     add ON CONFLICT DO NOTHING to INSERT commands
  --quote-all-identifiers      quote all identifiers, even if not key words
  --restrict-key=RESTRICT_KEY  use provided string as psql \restrict key
  --rows-per-insert=NROWS      number of rows per INSERT; implies --inserts
  --use-set-session-authorization
                               use SET SESSION AUTHORIZATION commands instead of
                               ALTER OWNER commands to set ownership

Connection options:
  -d, --dbname=CONNSTR     connect using connection string
  -h, --host=HOSTNAME      database server host or socket directory
  -l, --database=DBNAME    alternative default database
  -p, --port=PORT          database server port number
  -U, --username=NAME      connect as specified database user
  -w, --no-password        never prompt for password
  -W, --password           force password prompt (should happen automatically)
  --role=ROLENAME          do SET ROLE before dump

If -f/--file is not used, then the SQL script will be written to the standard
output.

Report bugs to <pgsql-bugs@lists.postgresql.org>.
PostgreSQL home page: <https://www.postgresql.org/>
[postgres@lxtrdpgdsgv01 ~]$

 

0. Introduction

Note: pg_dumpall does not support custom format backups.

The pg_dumpall utility is used to back up an entire PostgreSQL environment, including:

* Roles and users
* Tablespaces
* All databases (schemas and data)

It is especially useful for:

* Full cluster migrations
* Disaster recovery
* Environment replication across dev, QA, and prod

When restoring to a different host, you'll need to:

* Update tablespace paths (using tools like sed)
* Pre-create required tablespace directories

This ensures compatibility and successful restoration across different environments.

Backup


1. Backup ALL databases

[postgres@lxtrdpgdsgv01 ~]$ nohup pg_dumpall -U postgres -v -f /pgBackup/pgsql15/backup/backup_all_databases_10OCT2025.sql > /pgBackup/pgsql15/backup/backup_all_databases_10OCT2025.log 2>&1 &
[1] 5610
[postgres@lxtrdpgdsgv01 ~]$ 
[postgres@lxtrdpgdsgv01 ~]$ cat /pgBackup/pgsql15/backup/backup_all_databases_10OCT2025.log | grep -i /pgBackup/pgsql15/backup/backup_all_databases_10OCT2025.sql
pg_dumpall: running ""/usr/pgsql-15/bin/pg_dump"  -v -f /pgBackup/pgsql15/backup/backup_all_databases_10OCT2025.sql  -Fa 'user=postgres dbname=template1'"
pg_dumpall: running ""/usr/pgsql-15/bin/pg_dump"  -v -f /pgBackup/pgsql15/backup/backup_all_databases_10OCT2025.sql --create -Fa 'user=postgres dbname=edpua'"
pg_dumpall: running ""/usr/pgsql-15/bin/pg_dump"  -v -f /pgBackup/pgsql15/backup/backup_all_databases_10OCT2025.sql --create -Fa 'user=postgres dbname=gebua'"
pg_dumpall: running ""/usr/pgsql-15/bin/pg_dump"  -v -f /pgBackup/pgsql15/backup/backup_all_databases_10OCT2025.sql --create -Fa 'user=postgres dbname=orcl'"
pg_dumpall: running ""/usr/pgsql-15/bin/pg_dump"  -v -f /pgBackup/pgsql15/backup/backup_all_databases_10OCT2025.sql  -Fa 'user=postgres dbname=postgres'"
[postgres@lxtrdpgdsgv01 ~]$

[postgres@lxtrdpgdsgv01 ~]$ psql
psql (15.14)
Type "help" for help.

postgres=# \c orcl
You are now connected to database "orcl" as user "postgres".
orcl=# SELECT
orcl-#     schemaname || '.' || relname AS table_name,
orcl-#     pg_size_pretty(pg_total_relation_size(relid)) AS total_size,
orcl-#     pg_size_pretty(pg_relation_size(relid)) AS table_size,
orcl-#     pg_size_pretty(pg_total_relation_size(relid) - pg_relation_size(relid)) AS index_size
orcl-# FROM
orcl-#     pg_catalog.pg_statio_user_tables
orcl-# ORDER BY
orcl-#     pg_total_relation_size(relid) DESC;
    table_name    | total_size | table_size | index_size
------------------+------------+------------+------------
 trd.metrics_high | 799 MB     | 498 MB     | 301 MB
 trd.metrics_mid  | 638 MB     | 398 MB     | 240 MB
 trd.employees    | 493 MB     | 322 MB     | 172 MB
 trd.sales_2023   | 399 MB     | 249 MB     | 150 MB
 trd.sales_2024   | 399 MB     | 249 MB     | 150 MB
 trd.sales_2022   | 399 MB     | 249 MB     | 150 MB
 trd.sales_2021   | 398 MB     | 248 MB     | 150 MB
 trd.metrics_low  | 159 MB     | 99 MB      | 60 MB
 trd.test_data    | 71 MB      | 50 MB      | 21 MB
 trd.emp_summary  | 24 kB      | 8192 bytes | 16 kB
 trd.metrics_rest | 8192 bytes | 0 bytes    | 8192 bytes
(11 rows)

orcl=#


2. Backup users/roles definition

[postgres@lxtrdpgdsgv01 ~]$ nohup pg_dumpall -U postgres --roles-only -v -f /pgBackup/pgsql15/backup/roles.sql > /pgBackup/pgsql15/backup/roles.log 2>&1 &
[1] 5205
[postgres@lxtrdpgdsgv01 ~]$


3. Backup tablespaces definition

[postgres@lxtrdpgdsgv01 ~]$ nohup pg_dumpall -U postgres --tablespaces-only -v -f /pgBackup/pgsql15/backup/tablespaces.sql > /pgBackup/pgsql15/backup/tablespaces.log 2>&1 &
[1] 5183
[postgres@lxtrdpgdsgv01 ~]$


4. Backup dump only the schema, no data

[postgres@lxtrdpgdsgv01 ~]$ nohup pg_dumpall -U postgres --schema-only -v -f /pgBackup/pgsql15/backup/schemas.sql > /pgBackup/pgsql15/backup/schemas.log 2>&1 &
[1] 4890
[postgres@lxtrdpgdsgv01 ~]$ 


5. Backup dump only the data, not the schema

[postgres@lxtrdpgdsgv01 ~]$ nohup pg_dumpall -U postgres --data-only -v -f /pgBackup/pgsql15/backup/dataonly.sql > /pgBackup/pgsql15/backup/dataonly.log 2>&1 &
[1] 5233
[postgres@lxtrdpgdsgv01 ~]$ 


6. Backup dump data as INSERT commands, rather than COPY

[postgres@lxtrdpgdsgv01 ~]$ nohup pg_dumpall -U postgres --inserts -v -f /pgBackup/pgsql15/backup/inserts.sql > /pgBackup/pgsql15/backup/inserts.log 2>&1 &
[1] 5274
[postgres@lxtrdpgdsgv01 ~]$


7. Backup dump only global objects, no databases

[postgres@lxtrdpgdsgv01 ~]$ nohup pg_dumpall -U postgres --globals-only -v -f /pgBackup/pgsql15/backup/globals.sql > /pgBackup/pgsql15/backup/globals.log 2>&1 &
[1] 5331
[postgres@lxtrdpgdsgv01 ~]$

Restore


8. Restore on same host


A. Drop Existing Databases (Optional)

 

[postgres@lxtrdpgdsgv01 ~]$ psql
psql (15.14)
Type "help" for help.

postgres=# \l
                                                 List of databases
   Name    |  Owner   | Encoding |   Collate   |    Ctype    | ICU Locale | Locale Provider |   Access privileges
-----------+----------+----------+-------------+-------------+------------+-----------------+-----------------------
 edpua     | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |            | libc            |
 gebua     | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |            | libc            |
 orcl      | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |            | libc            |
 postgres  | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |            | libc            |
 template0 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |            | libc            | =c/postgres          +
           |          |          |             |             |            |                 | postgres=CTc/postgres
 template1 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |            | libc            | postgres=CTc/postgres+
           |          |          |             |             |            |                 | =c/postgres
(6 rows)

postgres=# drop database edpua;
DROP DATABASE
postgres=# drop database gebua;
DROP DATABASE
postgres=# drop database orcl;
DROP DATABASE
postgres=# \l
                                                 List of databases
   Name    |  Owner   | Encoding |   Collate   |    Ctype    | ICU Locale | Locale Provider |   Access privileges
-----------+----------+----------+-------------+-------------+------------+-----------------+-----------------------
 postgres  | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |            | libc            |
 template0 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |            | libc            | =c/postgres          +
           |          |          |             |             |            |                 | postgres=CTc/postgres
 template1 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |            | libc            | postgres=CTc/postgres+
           |          |          |             |             |            |                 | =c/postgres
(3 rows)

postgres=#

postgres=# \db
             List of tablespaces
    Name    |  Owner   |      Location
------------+----------+---------------------
 edpua_ix   | postgres | /pgIx/pgsql15/edpua
 edpua_tb   | postgres | /pgTb/pgsql15/edpua
 gebua_ix   | postgres | /pgIx/pgsql15/gebua
 gebua_tb   | postgres | /pgTb/pgsql15/gebua
 orcl_ix    | postgres | /pgIx/pgsql15/orcl
 orcl_tb    | postgres | /pgTb/pgsql15/orcl
 pg_default | postgres |
 pg_global  | postgres |
(8 rows)

postgres=#


B. Restore Full Backup

[postgres@lxtrdpgdsgv01 ~]$ nohup psql -U postgres -X -f /pgBackup/pgsql15/backup/backup_all_databases_10OCT2025.sql -d postgres > /pgBackup/pgsql15/backup/backup_all_databases_10OCT2025_restore.log
[1] 4132
[postgres@lxtrdpgdsgv01 ~]$ 

-- OR --

nohup psql -U postgres -f /pgBackup/pgsql15/backup/backup_all_databases_10OCT2025.sql > /pgBackup/pgsql15/backup/backup_all_databases_10OCT2025_restore.log 2>&1 &

-- Log: backup_all_databases_10OCT2025_restore.log


C. Verification

[postgres@lxtrdpgdsgv01 ~]$ psql
psql (15.14)
Type "help" for help.

postgres=# \l
                                                 List of databases
   Name    |  Owner   | Encoding |   Collate   |    Ctype    | ICU Locale | Locale Provider |   Access privileges
-----------+----------+----------+-------------+-------------+------------+-----------------+-----------------------
 edpua     | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |            | libc            |
 gebua     | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |            | libc            |
 orcl      | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |            | libc            |
 postgres  | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |            | libc            |
 template0 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |            | libc            | =c/postgres          +
           |          |          |             |             |            |                 | postgres=CTc/postgres
 template1 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |            | libc            | postgres=CTc/postgres+
           |          |          |             |             |            |                 | =c/postgres
(6 rows)

postgres=#


9. Restore to Another Host (Different Tablespace Paths)

A. Copy Backup File

[postgres@lxtrdpgdsgv01 backup]$ scp backup_all_databases_10OCT2025.sql 192.168.2.31:/pgBackup/pgsql15/backup/
postgres@192.168.2.31's password:
backup_all_databases_10OCT2025.sql                 100% 3556MB  51.5MB/s   01:09
[postgres@lxtrdpgdsgv01 backup]$ 

[postgres@pg17 backup]$ ls -ltr backup_all_databases_10OCT2025.sql
-rw-r--r--. 1 postgres postgres 3729147646 Oct  6 06:17 backup_all_databases_10OCT2025.sql
[postgres@pg17 backup]$


B. Extract Tablespace/Database Info

[postgres@lxtrdpgdsgv01 backup]$ grep -i "CREATE TABLESPACE" /pgBackup/pgsql15/backup/backup_all_databases_10OCT2025.sql
CREATE TABLESPACE orcl_tb OWNER postgres LOCATION '/pgTb/pgsql15/orcl';
CREATE TABLESPACE orcl_ix OWNER postgres LOCATION '/pgIx/pgsql15/orcl';
CREATE TABLESPACE gebua_tb OWNER postgres LOCATION '/pgTb/pgsql15/gebua';
CREATE TABLESPACE gebua_ix OWNER postgres LOCATION '/pgIx/pgsql15/gebua';
CREATE TABLESPACE edpua_tb OWNER postgres LOCATION '/pgTb/pgsql15/edpua';
CREATE TABLESPACE edpua_ix OWNER postgres LOCATION '/pgIx/pgsql15/edpua';
[postgres@lxtrdpgdsgv01 backup]$
[postgres@lxtrdpgdsgv01 backup]$ grep -i "CREATE DATABASE" /pgBackup/pgsql15/backup/backup_all_databases_10OCT2025.sql
CREATE DATABASE edpua WITH TEMPLATE = template0 ENCODING = 'UTF8' LOCALE_PROVIDER = libc LOCALE = 'en_US.UTF-8' TABLESPACE = edpua_tb;
CREATE DATABASE gebua WITH TEMPLATE = template0 ENCODING = 'UTF8' LOCALE_PROVIDER = libc LOCALE = 'en_US.UTF-8' TABLESPACE = gebua_tb;
CREATE DATABASE orcl WITH TEMPLATE = template0 ENCODING = 'UTF8' LOCALE_PROVIDER = libc LOCALE = 'en_US.UTF-8' TABLESPACE = orcl_tb;
[postgres@lxtrdpgdsgv01 backup]$


C. Create Tablespace Directories on Target

[postgres@pg17 ~]$ psql
psql (15.13)
Type "help" for help.

postgres=# \l
                                                 List of databases
   Name    |  Owner   | Encoding |   Collate   |    Ctype    | ICU Locale | Locale Provider |   Access privileges
-----------+----------+----------+-------------+-------------+------------+-----------------+-----------------------
 postgres  | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |            | libc            |
 template0 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |            | libc            | =c/postgres          +
           |          |          |             |             |            |                 | postgres=CTc/postgres
 template1 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |            | libc            | postgres=CTc/postgres+
           |          |          |             |             |            |                 | =c/postgres
(3 rows)

postgres=#
postgres=# \db
       List of tablespaces
    Name    |  Owner   | Location
------------+----------+----------
 pg_default | postgres |
 pg_global  | postgres |
(2 rows)

postgres=#


# Create Directory 

[postgres@pg17 ~]$ mkdir -p /pgData/pgsql15/orcl_tb
[postgres@pg17 ~]$ mkdir -p /pgData/pgsql15/orcl_ix
[postgres@pg17 ~]$ mkdir -p /pgData/pgsql15/gebua_tb
[postgres@pg17 ~]$ mkdir -p /pgData/pgsql15/gebua_ix
[postgres@pg17 ~]$ mkdir -p /pgData/pgsql15/edpua_tb
[postgres@pg17 ~]$ mkdir -p /pgData/pgsql15/edpua_ix


D. Create Tablespaces in PostgreSQL

postgres=# CREATE TABLESPACE orcl_tb OWNER postgres LOCATION  '/pgData/pgsql15/orcl_tb';
CREATE TABLESPACE
postgres=# CREATE TABLESPACE orcl_ix OWNER postgres LOCATION  '/pgData/pgsql15/orcl_ix';
CREATE TABLESPACE
postgres=# CREATE TABLESPACE gebua_tb OWNER postgres LOCATION '/pgData/pgsql15/gebua_tb';
CREATE TABLESPACE
postgres=# CREATE TABLESPACE gebua_ix OWNER postgres LOCATION '/pgData/pgsql15/gebua_ix';
CREATE TABLESPACE
postgres=# CREATE TABLESPACE edpua_tb OWNER postgres LOCATION '/pgData/pgsql15/edpua_tb';
CREATE TABLESPACE
postgres=# CREATE TABLESPACE edpua_ix OWNER postgres LOCATION '/pgData/pgsql15/edpua_ix';
CREATE TABLESPACE
postgres=#


-- OR --- 
 You can modify the tablespace paths directly in the backup file; however, this approach is not recommended for large backup files due to  reliability concerns.

cd /pgBackup/pgsql15/backup/
# Replace ORCL paths
sed -i 's|/pgTb/pgsql15/orcl|/pgData/pgsql15/orcl_tb|g' backup_all_databases_10OCT2025.sql
sed -i 's|/pgIx/pgsql15/orcl|/pgData/pgsql15/orcl_ix|g' backup_all_databases_10OCT2025.sql

# Replace GEBUA paths
sed -i 's|/pgTb/pgsql15/gebua|/pgData/pgsql15/gebua_tb|g' backup_all_databases_10OCT2025.sql
sed -i 's|/pgIx/pgsql15/gebua|/pgData/pgsql15/gebua_ix|g' backup_all_databases_10OCT2025.sql

# Replace EDPUA paths
sed -i 's|/pgTb/pgsql15/edpua|/pgData/pgsql15/edpua_tb|g' backup_all_databases_10OCT2025.sql
sed -i 's|/pgIx/pgsql15/edpua|/pgData/pgsql15/edpua_ix|g' backup_all_databases_10OCT2025.sql


[postgres@pg17 ~]$ psql
psql (15.13)
Type "help" for help.

postgres=# \db
               List of tablespaces
    Name    |  Owner   |         Location
------------+----------+--------------------------
 edpua_ix   | postgres | /pgData/pgsql15/edpua_ix
 edpua_tb   | postgres | /pgData/pgsql15/edpua_tb
 gebua_ix   | postgres | /pgData/pgsql15/gebua_ix
 gebua_tb   | postgres | /pgData/pgsql15/gebua_tb
 orcl_ix    | postgres | /pgData/pgsql15/orcl_ix
 orcl_tb    | postgres | /pgData/pgsql15/orcl_tb
 pg_default | postgres |
 pg_global  | postgres |
(8 rows)

postgres=# 


E. Optional: Backup on Target Host

[postgres@pg17 ~]$ nohup pg_dumpall -U postgres -v -f /pgBackup/pgsql15/backup/backup_all_databases_10OCT2025_pg17.sql > /pgBackup/pgsql15/backup/backup_all_databases_10OCT2025_pg17.log 2>&1 &
[1] 4246
[postgres@pg17 ~]$


F. Restore on Target Host

[postgres@pg17 ~]$ nohup psql -U postgres -X -f /pgBackup/pgsql15/backup/backup_all_databases_10OCT2025.sql -d postgres > /pgBackup/pgsql15/backup/backup_all_databases_10OCT2025_restore_pg17.log 2>&1 &
[1] 5213
[postgres@pg17 ~]$ 

-- OR --

nohup psql -U postgres -f /pgBackup/pgsql15/backup/backup_all_databases_10OCT2025.sql > /pgBackup/pgsql15/backup/backup_all_databases_10OCT2025_restore_pg17.log 2>&1 &

-- Log: backup_all_databases_10OCT2025_restore_pg17.log


G. Final Verification

[postgres@pg17 ~]$ psql
psql (15.13)
Type "help" for help.

postgres=# \l
List of databases
Name | Owner | Encoding | Collate | Ctype | ICU Locale | Locale Provider | Access privileges
-----------+----------+----------+-------------+-------------+------------+-----------------+-----------------------
 edpua | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | | libc |
gebua | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | | libc |
orcl | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | | libc |
postgres | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | | libc |
template0 | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | | libc | =c/postgres +
| | | | | | | postgres=CTc/postgres
template1 | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | | libc | postgres=CTc/postgres+
| | | | | | | =c/postgres
(6 rows)

postgres=#

[postgres@pg17 ~]$ psql
psql (15.13)
Type "help" for help.

postgres=# \c orcl
You are now connected to database "orcl" as user "postgres".
orcl=# SELECT
orcl-# schemaname || '.' || relname AS table_name,
orcl-# pg_size_pretty(pg_total_relation_size(relid)) AS total_size,
orcl-# pg_size_pretty(pg_relation_size(relid)) AS table_size,
orcl-# pg_size_pretty(pg_total_relation_size(relid) - pg_relation_size(relid)) AS index_size
orcl-# FROM
orcl-# pg_catalog.pg_statio_user_tables
orcl-# ORDER BY
orcl-# pg_total_relation_size(relid) DESC;
 table_name | total_size | table_size | index_size
------------------+------------+------------+------------
trd.metrics_high | 799 MB | 498 MB | 301 MB
trd.metrics_mid | 638 MB | 398 MB | 240 MB
trd.employees | 493 MB | 322 MB | 172 MB
trd.sales_2023 | 399 MB | 249 MB | 150 MB
trd.sales_2024 | 399 MB | 249 MB | 150 MB
trd.sales_2022 | 399 MB | 249 MB | 150 MB
trd.sales_2021 | 398 MB | 248 MB | 150 MB
trd.metrics_low | 159 MB | 99 MB | 60 MB
trd.test_data | 71 MB | 50 MB | 21 MB
trd.emp_summary | 24 kB | 8192 bytes | 16 kB
trd.metrics_rest | 8192 bytes | 0 bytes | 8192 bytes
(11 rows)

orcl=#

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/

PostgreSQL User Management

PostgreSQL User Management

Create Users, Groups and Schema Paths for PostgreSQL

Table of Contents


Step 1: Create a User
Step 2: Change User Password
Step 3: Grant Database Access
Step 4: Expire Password
Step 5: Set Password Never Expire
Step 6: Lock Account
Step 7: Unlock Account
Step 8: Create Schema
Step 9: Create Roles & Users
Step 10: Assign Ownership
Step 11: Grant Schema Privileges
Step 12: Grant RW Privileges
Step 13: Grant RO Privileges
Step 14: Assign Roles to Users
Step 15: Testing
Step 16: Set Schema Search Path
Step 17: Groups
Step 18: PostgreSQL — Table-View Privileges


The primary difference between CREATE ROLE and CREATE USER is that CREATE USER automatically includes the LOGIN privilege, allowing the role to connect to the database, whereas CREATE ROLE does not grant the LOGIN privilege unless it is explicitly specified.

PostgreSQL internally treats users and groups as roles. Therefore, using CREATE ROLE is often recommended. However, CREATE USER and CREATE GROUP are still supported and commonly used by DBAs. You can use whichever command you find easier to understand and manage.


Step 1: Create a User

-- Option 1: Using CREATE USER
CREATE USER john WITH PASSWORD 'mypassword';

-- Option 2: Using CREATE ROLE with LOGIN
CREATE ROLE john LOGIN PASSWORD 'mypassword';

postgres=# CREATE USER john WITH PASSWORD 'mypassword';
CREATE ROLE
postgres=# CREATE ROLE john LOGIN PASSWORD 'mypassword';
ERROR:  role "john" already exists



Step 2: Change User Password

Passwords can be changed by either an admin or the user.

By Admin:

postgres=# ALTER USER john WITH PASSWORD 'newpassword';
ALTER ROLE
postgres=#

-- OR --

postgres=# \password john
Enter new password for user "john":
Enter it again:
postgres=#


By User (self-service): From the psql prompt:

[postgres@pg17 ~]$ psql -h 192.168.2.31 -U john -d mydb -W
Password:

mydb=> \conninfo
You are connected to database "mydb" as user "john" on host "192.168.2.31" at port "5432".

mydb=> \password
Enter new password for user "john":
Enter it again:
mydb=>



Step 3: Grant Database Access

To allow a user to connect to a database:

postgres=# GRANT CONNECT ON DATABASE mydb TO john;
GRANT
postgres=#


Verify user login:

-- Connect as user
[postgres@pg17 ~]$ psql -h 192.168.2.31 -U john -d mydb -W
Password:

-- Check current user
mydb=> SELECT CURRENT_USER;
 current_user
--------------
 john
(1 row)

mydb=>
mydb=> select session_user;
 session_user
--------------
 john
(1 row)

-- Connection info
mydb=> \conninfo
You are connected to database "mydb" as user "john" on host "192.168.2.31" at port "5432".
mydb=>



Step 4: Expire User Password

postgres=# ALTER USER john VALID UNTIL '2025-09-11';
ALTER ROLE
postgres=#
postgres=# \du+
                                          List of roles
 Role name |                         Attributes                         | Member of | Description
-----------+------------------------------------------------------------+-----------+-------------
 john      | Password valid until 2025-09-11 00:00:00-04                | {}        |
 postgres  | Superuser, Create role, Create DB, Replication, Bypass RLS | {}        |

postgres=#



Step 5: Set Password to Never Expire

postgres=# \du
                                   List of roles
 Role name |                         Attributes                         | Member of
-----------+------------------------------------------------------------+-----------
 john      | Password valid until 2025-09-11 00:00:00-04                | {}
 postgres  | Superuser, Create role, Create DB, Replication, Bypass RLS | {}


-- Without changing existing password

postgres=# ALTER USER john VALID UNTIL 'infinity';
ALTER ROLE
postgres=#

-- With changing existing password

postgres=# ALTER USER john WITH PASSWORD 'newpassword' VALID UNTIL 'infinity';
ALTER ROLE
postgres=#
postgres=# \du
                                   List of roles
 Role name |                         Attributes                         | Member of
-----------+------------------------------------------------------------+-----------
 john      | Password valid until infinity                              | {}
 postgres  | Superuser, Create role, Create DB, Replication, Bypass RLS | {}


postgres=#

-- Set to future date

postgres=# ALTER USER john VALID UNTIL '2025-12-31';
ALTER ROLE
postgres=# \du+
                                          List of roles
 Role name |                         Attributes                         | Member of | Description
-----------+------------------------------------------------------------+-----------+-------------
 john      | Password valid until 2025-12-31 00:00:00-05                | {}        |
 postgres  | Superuser, Create role, Create DB, Replication, Bypass RLS | {}        |

postgres=#



Step 6: Lock User Account

postgres=# ALTER USER john NOLOGIN;
ALTER ROLE
postgres=# \du+
                                          List of roles
 Role name |                         Attributes                         | Member of | Description
-----------+------------------------------------------------------------+-----------+-------------
 john      | Cannot login                                              +| {}        |
           | Password valid until infinity                              |           |
 postgres  | Superuser, Create role, Create DB, Replication, Bypass RLS | {}        |

postgres=#



Step 7: Unlock User Account

postgres=# ALTER USER john LOGIN;
ALTER ROLE
postgres=# \du+
                                          List of roles
 Role name |                         Attributes                         | Member of | Description
-----------+------------------------------------------------------------+-----------+-------------
 john      | Password valid until infinity                              | {}        |
 postgres  | Superuser, Create role, Create DB, Replication, Bypass RLS | {}        |

postgres=#



Step 8: Create Schema

[postgres@pg17 ~]$ psql
psql (15.13)
Type "help" for help.

postgres=# \c mydb
You are now connected to database "mydb" as user "postgres".
mydb=#
mydb=# CREATE SCHEMA BLP;
CREATE SCHEMA
mydb=# \dn
      List of schemas
  Name  |       Owner
--------+-------------------
 blp    | postgres
 public | pg_database_owner
(2 rows)

mydb=#



Step 9: Create Roles & Users

postgres=# CREATE USER "BLP" WITH PASSWORD 'blp';
CREATE ROLE
postgres=# 
postgres=# CREATE ROLE blp_rw NOLOGIN;
CREATE ROLE
postgres=# CREATE ROLE blp_ro NOLOGIN;
CREATE ROLE
postgres=#

postgres=# CREATE USER alice WITH PASSWORD 'alice123';
CREATE ROLE
postgres=# CREATE USER bob WITH PASSWORD 'bob123';
CREATE ROLE
postgres=# CREATE USER charlie WITH PASSWORD 'charlie123';
CREATE ROLE
postgres=#

postgres=# \du+
                                          List of roles
 Role name |                         Attributes                         | Member of | Description
-----------+------------------------------------------------------------+-----------+-------------
 BLP       |                                                            | {}        |
 alice     |                                                            | {}        |
 blp_ro    | Cannot login                                               | {}        |
 blp_rw    | Cannot login                                               | {}        |
 bob       |                                                            | {}        |
 charlie   |                                                            | {}        |
 john      | Password valid until 2025-12-31 00:00:00-05                | {}        |
 postgres  | Superuser, Create role, Create DB, Replication, Bypass RLS | {}        |
 trduser   |                                                            | {}        |

postgres=#



Step 10: Assign Ownership on Schema

-- Please do NOT grant this privillege, Owner can drop the schema, change privileges, and has full control over all objects inside.

postgres=# \c mydb
You are now connected to database "mydb" as user "postgres".
mydb=#
mydb=# \dn
      List of schemas
  Name  |       Owner
--------+-------------------
 blp    | postgres
 public | pg_database_owner
(2 rows)

mydb=# ALTER SCHEMA BLP OWNER TO "BLP";
ALTER SCHEMA
mydb=#

mydb=# \dn+
                                       List of schemas
  Name  |       Owner       |           Access privileges            |      Description
--------+-------------------+----------------------------------------+------------------------
 blp    | BLP               |                                        |
 public | pg_database_owner | pg_database_owner=UC/pg_database_owner+| standard public schema
        |                   | =U/pg_database_owner                   |
(2 rows)

mydb=# 



Step 11: Grant Schema Privileges to Owner

-- Full control on schema: usage + create
GRANT USAGE, CREATE ON SCHEMA blp TO "BLP";

mydb=# \dn+
                                       List of schemas
  Name  |       Owner       |           Access privileges            |      Description
--------+-------------------+----------------------------------------+------------------------
 blp    | BLP               |                                        |
 public | pg_database_owner | pg_database_owner=UC/pg_database_owner+| standard public schema
        |                   | =U/pg_database_owner                   |
(2 rows)

mydb=# GRANT USAGE, CREATE ON SCHEMA blp TO "BLP";
GRANT
mydb=# \dn+
                                       List of schemas
  Name  |       Owner       |           Access privileges            |      Description
--------+-------------------+----------------------------------------+------------------------
 blp    | BLP               | BLP=UC/BLP                             |
 public | pg_database_owner | pg_database_owner=UC/pg_database_owner+| standard public schema
        |                   | =U/pg_database_owner                   |
(2 rows)

mydb=#



Step 12: Grant RW Privileges

USAGE → allows the role to see the schema and its objects.

-- Grant schema access without CREATE
GRANT USAGE ON SCHEMA BLP TO blp_rw;

-- Grant DML on all existing tables
GRANT SELECT, INSERT, UPDATE, DELETE ON ALL TABLES IN SCHEMA BLP TO blp_rw;

-- Future tables
ALTER DEFAULT PRIVILEGES IN SCHEMA BLP GRANT SELECT, INSERT, UPDATE, DELETE ON TABLES TO blp_rw;

mydb=# GRANT USAGE ON SCHEMA BLP TO blp_rw;
GRANT
mydb=# GRANT SELECT, INSERT, UPDATE, DELETE ON ALL TABLES IN SCHEMA BLP TO blp_rw;
GRANT
mydb=# ALTER DEFAULT PRIVILEGES IN SCHEMA BLP GRANT SELECT, INSERT, UPDATE, DELETE ON TABLES TO blp_rw;
ALTER DEFAULT PRIVILEGES
mydb=#
mydb=# \dn+
                                       List of schemas
  Name  |       Owner       |           Access privileges            |      Description
--------+-------------------+----------------------------------------+------------------------
 blp    | BLP               | BLP=UC/BLP                            +|
        |                   | blp_rw=U/BLP                           |
 public | pg_database_owner | pg_database_owner=UC/pg_database_owner+| standard public schema
        |                   | =U/pg_database_owner                   |
(2 rows)

mydb=#



Step 13: Grant RO Privileges

-- Grant schema access without CREATE
GRANT USAGE ON SCHEMA BLP TO BLP_RO;

-- Grant SELECT on all existing tables
GRANT SELECT ON ALL TABLES IN SCHEMA BLP TO BLP_RO;

-- Future tables
ALTER DEFAULT PRIVILEGES IN SCHEMA BLP GRANT SELECT ON TABLES TO BLP_RO;

mydb=# GRANT USAGE ON SCHEMA BLP TO BLP_RO;
GRANT
mydb=# GRANT SELECT ON ALL TABLES IN SCHEMA BLP TO BLP_RO;
GRANT
mydb=# ALTER DEFAULT PRIVILEGES IN SCHEMA BLP GRANT SELECT ON TABLES TO BLP_RO;
ALTER DEFAULT PRIVILEGES
mydb=#
mydb=# \dn+
                                       List of schemas
  Name  |       Owner       |           Access privileges            |      Description
--------+-------------------+----------------------------------------+------------------------
 blp    | BLP               | BLP=UC/BLP                            +|
        |                   | blp_rw=U/BLP                          +|
        |                   | blp_ro=U/BLP                           |
 public | pg_database_owner | pg_database_owner=UC/pg_database_owner+| standard public schema
        |                   | =U/pg_database_owner                   |
(2 rows)

mydb=#



Step 14: Assign Roles to Users

mydb=# GRANT BLP_RW TO ALICE;
GRANT ROLE
mydb=# 
mydb=# GRANT BLP_RO TO BOB,CHARLIE;
GRANT ROLE
mydb=#

mydb=# \du+
                                          List of roles
 Role name |                         Attributes                         | Member of | Description
-----------+------------------------------------------------------------+-----------+-------------
 BLP       |                                                            | {}        |
 alice     |                                                            | {blp_rw}  |
 blp_ro    | Cannot login                                               | {}        |
 blp_rw    | Cannot login                                               | {}        |
 bob       |                                                            | {blp_ro}  |
 charlie   |                                                            | {blp_ro}  |
 john      | Password valid until 2025-12-31 00:00:00-05                | {}        |
 postgres  | Superuser, Create role, Create DB, Replication, Bypass RLS | {}        |
 trduser   |                                                            | {}        |

mydb=# 



Step 15: Testing

-- Login to BLP user on mydb database and create table on blp schema. 

[postgres@pg17 ~]$ psql -h 192.168.2.31 -U BLP -d mydb -W
Password:
psql (15.13)
Type "help" for help.

mydb=> \conninfo
You are connected to database "mydb" as user "BLP" on host "192.168.2.31" at port "5432".
mydb=> CREATE TABLE blp.employees (
mydb(>     emp_id SERIAL PRIMARY KEY,
mydb(>     first_name VARCHAR(50),
mydb(>     last_name VARCHAR(50),
mydb(>     hire_date DATE,
mydb(>     salary NUMERIC(10,2)
mydb(> );
CREATE TABLE
mydb=>

mydb=> INSERT INTO blp.employees (first_name, last_name, hire_date, salary) VALUES
mydb-> ('John', 'Doe', '2023-01-15', 5000.00),
mydb-> ('Jane', 'Smith', '2022-11-20', 6000.00),
mydb-> ('Alice', 'Johnson', '2024-03-01', 5500.00);
INSERT 0 3
mydb=>
mydb=> select * from blp.employees;
 emp_id | first_name | last_name | hire_date  | salary
--------+------------+-----------+------------+---------
      1 | John       | Doe       | 2023-01-15 | 5000.00
      2 | Jane       | Smith     | 2022-11-20 | 6000.00
      3 | Alice      | Johnson   | 2024-03-01 | 5500.00
(3 rows)

mydb=>

mydb=> drop table blp.employees;
DROP TABLE
mydb=>

-- Login to alice user on mydb database and update table on blp schema. 



[root@pg17 ~]# psql -h 192.168.2.31 -U alice -d mydb -W
Password:
psql (15.13)
Type "help" for help.

mydb=> \conninfo
You are connected to database "mydb" as user "alice" on host "192.168.2.31" at port "5432".
mydb=>

mydb=> \du+ alice
                  List of roles
 Role name | Attributes | Member of | Description
-----------+------------+-----------+-------------
 alice     |            | {blp_rw}  |

mydb=>


mydb=> \dt+ blp.*
                                      List of relations
 Schema |   Name    | Type  | Owner | Persistence | Access method |    Size    | Description
--------+-----------+-------+-------+-------------+---------------+------------+-------------
 blp    | employees | table | BLP   | permanent   | heap          | 8192 bytes |
(1 row)

mydb=> select * from blp.employees;
 emp_id | first_name | last_name | hire_date  | salary
--------+------------+-----------+------------+---------
      1 | John       | Doe       | 2023-01-15 | 5000.00
      2 | Jane       | Smith     | 2022-11-20 | 6000.00
      3 | Alice      | Johnson   | 2024-03-01 | 5500.00
(3 rows)

mydb=> UPDATE blp.employees
SET salary = CASE
                WHEN first_name = 'John' THEN 7000.00
                WHEN first_name = 'Alice' THEN 6500.00
             END
WHERE first_name IN ('John', 'Alice');
UPDATE 2
mydb=> select * from blp.employees;
 emp_id | first_name | last_name | hire_date  | salary
--------+------------+-----------+------------+---------
      2 | Jane       | Smith     | 2022-11-20 | 6000.00
      1 | John       | Doe       | 2023-01-15 | 7000.00
      3 | Alice      | Johnson   | 2024-03-01 | 6500.00
(3 rows)

mydb=>

-- Note, we have granted only DML privilleges, hence create and alter table command failing

mydb=> CREATE TABLE blp.departments (
mydb(>     dept_id SERIAL PRIMARY KEY,
mydb(>     dept_name VARCHAR(100) NOT NULL,
mydb(>     location VARCHAR(100)
mydb(> );
ERROR:  permission denied for schema blp
LINE 1: CREATE TABLE blp.departments (
                     ^
mydb=>

mydb=> ALTER TABLE blp.employees
mydb-> ADD COLUMN department VARCHAR(50);
ERROR:  must be owner of table employees
mydb=>

-- Login to bob user on mydb database and select table on blp schema. 

[postgres@pg17 ~]$ psql -h 192.168.2.31 -U bob -d mydb -W
Password:
psql (15.13)
Type "help" for help.

mydb=> \conninfo
You are connected to database "mydb" as user "bob" on host "192.168.2.31" at port "5432".
mydb=>
mydb=> \du+ bob
                  List of roles
 Role name | Attributes | Member of | Description
-----------+------------+-----------+-------------
 bob       |            | {blp_ro}  |

mydb-> \dt+ blp.*
                                      List of relations
 Schema |   Name    | Type  | Owner | Persistence | Access method |    Size    | Description
--------+-----------+-------+-------+-------------+---------------+------------+-------------
 blp    | employees | table | BLP   | permanent   | heap          | 8192 bytes |
(1 row)

mydb=> select * from blp.employees;
 emp_id | first_name | last_name | hire_date  | salary
--------+------------+-----------+------------+---------
      2 | Jane       | Smith     | 2022-11-20 | 6000.00
      1 | John       | Doe       | 2023-01-15 | 7000.00
      3 | Alice      | Johnson   | 2024-03-01 | 6500.00
(3 rows)

mydb=>

mydb=> INSERT INTO blp.employees (first_name, last_name, hire_date, salary) VALUES
mydb-> ('Bob', 'Williams', '2024-04-01', 5800.00),
mydb-> ('Clara', 'Brown', '2024-05-10', 6200.00),
mydb-> ('David', 'Lee', '2024-06-15', 5300.00);
ERROR:  permission denied for table employees
mydb=>



Step 16: Set Schema Search Path

[postgres@pg17 ~]$ psql -h 192.168.2.31 -U BLP -d mydb -W
Password:
psql (15.13)
Type "help" for help.

mydb=> 
mydb=> \conninfo
You are connected to database "mydb" as user "BLP" on host "192.168.2.31" at port "5432".
mydb=>
mydb=> \dt+ blp.*
                                      List of relations
 Schema |   Name    | Type  | Owner | Persistence | Access method |    Size    | Description
--------+-----------+-------+-------+-------------+---------------+------------+-------------
 blp    | employees | table | BLP   | permanent   | heap          | 8192 bytes |
(1 row)

mydb=> 

mydb=> select * from employees;
ERROR:  relation "employees" does not exist
LINE 1: select * from employees;
mydb=>

mydb=> SET search_path to BLP; -- Temporarily for this session
SET
mydb=> select * from employees;
 emp_id | first_name | last_name | hire_date  | salary
--------+------------+-----------+------------+---------
      2 | Jane       | Smith     | 2022-11-20 | 6000.00
      1 | John       | Doe       | 2023-01-15 | 7000.00
      3 | Alice      | Johnson   | 2024-03-01 | 6500.00
(3 rows)

mydb=>

-- Make the Schema Default for the user BLP -- Permenant
ALTER ROLE blp_owner SET search_path = BLP;


Step 17: Groups

postgres=# CREATE GROUP app_users;
postgres=# ALTER GROUP app_users ADD USER alice;
postgres=# ALTER GROUP app_users ADD USER bob;
postgres=# ALTER GROUP app_users ADD USER charlie;
postgres=# ALTER GROUP app_users DROP USER charlie;
postgres=# ALTER GROUP app_users RENAME TO appusers;
postgres=# DROP GROUP appusers;

mydb=> select * from pg_group;
          groname          | grosysid |    grolist
---------------------------+----------+---------------
 pg_database_owner         |     6171 | {}
 pg_read_all_data          |     6181 | {}
 pg_write_all_data         |     6182 | {}
 pg_monitor                |     3373 | {}
 pg_read_all_settings      |     3374 | {3373}
 pg_read_all_stats         |     3375 | {3373}
 pg_stat_scan_tables       |     3377 | {3373}
 pg_read_server_files      |     4569 | {}
 pg_write_server_files     |     4570 | {}
 pg_execute_server_program |     4571 | {}
 pg_signal_backend         |     4200 | {}
 pg_checkpoint             |     4544 | {}
 blp_rw                    |    84444 | {84447}
 blp_ro                    |    84445 | {84448,84449}
 app_users                 |    84468 | {}
(15 rows)

mydb=>



Step 18: PostgreSQL Object-Level Privilege Summary

mydb=> \z blp.employees
                               Access privileges
 Schema |   Name    | Type  | Access privileges | Column privileges | Policies
--------+-----------+-------+-------------------+-------------------+----------
 blp    | employees | table | BLP=arwdDxt/BLP  +|                   |
        |           |       | blp_ro=r/BLP     +|                   |
        |           |       | blp_rw=arwd/BLP   |                   |
(1 row)

Example:

 

ShortFull PrivilegeExample GRANT
rSELECTGRANT SELECT ON employees TO hr_user;
aINSERTGRANT INSERT ON employees TO hr_user;
wUPDATEGRANT UPDATE ON employees TO hr_user;
dDELETEGRANT DELETE ON employees TO hr_user;
DTRUNCATEGRANT TRUNCATE ON employees TO hr_user;
xREFERENCESGRANT REFERENCES ON employees TO hr_user;
tTRIGGERGRANT TRIGGER ON employees TO hr_user;
RRULEGRANT RULE ON employees TO hr_user; (rarely used)

 

Tip: the shorthand string you see in \z (for example arwdDxt) can be expanded by mapping each letter to the rows above, then converting them into one or more GRANT statements.

 

 

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
WhatsApp : 
Linkedin: https://www.linkedin.com/in/rajasekhar-amudala/

 

PSQL

PostgreSQL DBA Step by Step Learning

#PostgreSQL DBA Topics
1How to Install PostgreSQL ON Linux?
2How to Install PostgreSQL on Linux 7 using source code?
3How to START/STOP PostgreSQL ON Linux?
4How to Create Database in PostgreSQL?
5PostgreSQL User Management
6PostgreSQL pg_hba.conf Guide
7PostgreSQL Change Data Directory
8Understanding WAL Files in PostgreSQL – For Oracle DBAs
9Change PostgreSQL WAL Directory Path (pg_wal)
10Enable Archive Mode in PostgreSQL 17
11How to Disable ARCHIVELOG Mode
12PostgreSQL Tablespace Management
13PostgreSQL pg_dump and pg_restore Guide
14PostgreSQL Backup and Restore Using pg_dumpall and psql
15pg_basebackup – Backup, Restore, and Recovery
16Backup & Restore PostgreSQL DB Cluster to Another Host (No Archive Mode)
17Backup & Restore PostgreSQL DB Cluster on Same Host
18Restore PostgreSQL to New Host using pg_basebackup + WAL Archives
19PostgreSQL PITR – Point in Time Recovery
20Configure Streaming Replication in PostgreSQL
21Manual Failover in PostgreSQL Streaming Replication
22Convert Asynchronous Replication to Synchronous Replication

 

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