01 Lesson 01: Basic Tools / Installation and Management, psql

Page 1: Basic Tools / Installation and Management, psql

Copyright

© Postgres Professional, 2017–2025 Authors: Egor Rogov, Pavel Luzanov, Ilya Bashtanov, Igor Gnatyuk Translated by: Liudmila Mantrova, Alexander Meleshko, Elena Sharafutdinova Photo by: Oleg Bartunov (Phu monastery, Bhrikuti summit, Nepal)

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Page 2: Topics

• PostgreSQL Installation Types
• Server Management
• Server Message Log
• Configuration Parameters
• Using psql

Page 3: Database Cluster

{#source-figure-003 caption=“Source slide page 3: Database Cluster”}

• client

Speaker notes

Let’s start with the general concepts.

PostgreSQL is a program that belongs to the class of database management systems.

When this program is running, we call it a PostgreSQL server or a server instance. So far, the server seems to be a “black box” for us, but gradually we will get acquainted with how it works.

The data managed by PostgreSQL is stored in databases. One instance of PostgreSQL simultaneously manages several databases. This set of databases is called a database cluster. We will talk more about databases in the “Data organization. Logical structure” lesson.

The server interacts with clients. Clients are external applications that can connect to server databases and send queries for execution.

To summarize: a database cluster is the data in files; a server or a server instance is a program that manages the database cluster; a client is an application that “talks” to the server.

Page 4: Installation

Installation types

• pre-build packages (preferred)
• installation from source code
• without installation (cloud services)
• Extensions
  • provide additional features
  • installed separately
  • shipped with the server as modules and programs (~50 extensions)

Speaker notes

The preferred option for installing PostgreSQL is via a package manager (such as apt or rpm) using pre-built packages. This gives you a comprehensive installation that is easy to support and upgrade. There are packages available for most operating systems.

Another option is to build PostgreSQL from source code. This may be necessary if you want to set up a non-standard configuration or deploy on an exotic platform.

Pre-built packages and source codes: http://www.postgresql.org/download/

Besides, you can work with cloud-based managed databases that do not require any installation at all. Such ready-to-use services are provided by all major cloud platforms (Amazon RDS, Google Cloud SQL, Microsoft Azure).

In this course, we are going to use a virtual machine with Xubuntu 24 OS; PostgreSQL 16 is installed from the package for this OS. In addition, the installation is set up to start and stop PostgreSQL when the OS starts and stops.

There are a lot of PostgreSQL extensions that add new database functionality “on the fly”, without modifying the system core. About 50 extensions are included into the PostgreSQL distribution itself.

https://postgrespro.com/docs/postgresql/16/contrib

https://postgrespro.com/docs/postgresql/16/contrib-prog

The list of available extensions and their installation status can be accessed using the pg_available_extensions view.

Page 5: Server Management

Management tools

• pg_ctlcluster
• pg_ctl
• Main operations
  • start the server
  • stop the server
  • reload configuration parameters

Speaker notes

The main server management tasks are: initializing the database cluster, starting and stopping the server, reloading configuration parameters, and a few others. To perform these actions, use the pg_ctl utility, which comes together with PostgreSQL.

In the Ubuntu PostgreSQL package, pg_ctl is not run directly, but through a special wrapper pg_ctlcluster. The help information for pg_ctlcluster can be viewed using man:

$ man pg_ctlcluster

Information about existing clusters and their status can be obtained using the following commands:

$ pg_lsclusters

$ pg_ctlcluster status

For more details about server management for database administrators, see:

https://postgrespro.com/docs/postgresql/16/app-pg-ctl

https://postgrespro.com/docs/postgresql/16/runtime

Page 6: Installation and Management

PostgreSQL in the course VM is installed from packages. PostgreSQL installation directory:

student$ ls -l /usr/lib/postgresql/16

total 8
drwxr-xr-x 2 root root 4096 Nov 27 12:16 bin
drwxr-xr-x 4 root root 4096 Nov 27 13:14 lib

The owner of the server software is the root user. The database cluster is automatically initialized when installed from a package and is located in the /var/lib/postgresql/16/main directory. This directory will be referred to as PGDATA in subsequent topics. The owner of the directory is postgres. Here is what the directory contains:

student$ sudo ls -l /var/lib/postgresql/16/main

total 96
drwx------ 1 postgres postgres 4096 Nov 27 14:17 base
drwx------ 1 postgres postgres 4096 Nov 27 14:17 global
drwx------ 2 postgres postgres 4096 Nov 27 13:14 pg_commit_ts
drwx------ 2 postgres postgres 4096 Nov 27 13:14 pg_dynshmem
drwx------ 4 postgres postgres 4096 Nov 27 13:16 pg_logical
drwx------ 4 postgres postgres 4096 Nov 27 13:14 pg_multixact
drwx------ 2 postgres postgres 4096 Nov 27 13:14 pg_notify
drwx------ 2 postgres postgres 4096 Nov 27 13:14 pg_replslot
drwx------ 2 postgres postgres 4096 Nov 27 13:14 pg_serial
drwx------ 2 postgres postgres 4096 Nov 27 13:14 pg_snapshots
drwx------ 1 postgres postgres 4096 Nov 27 14:17 pg_stat
drwx------ 2 postgres postgres 4096 Nov 27 13:14 pg_stat_tmp
drwx------ 2 postgres postgres 4096 Nov 27 13:14 pg_subtrans
drwx------ 2 postgres postgres 4096 Nov 27 13:14 pg_tblspc
drwx------ 2 postgres postgres 4096 Nov 27 13:14 pg_twophase
-rw------- 1 postgres postgres    3 Nov 27 13:14 PG_VERSION
drwx------ 1 postgres postgres 4096 Nov 27 13:14 pg_wal
drwx------ 2 postgres postgres 4096 Nov 27 13:14 pg_xact
-rw------- 1 postgres postgres   88 Nov 27 13:14 postgresql.auto.conf
-rw------- 1 postgres postgres  130 Nov 27 14:17 postmaster.opts
-rw------- 1 postgres postgres  108 Nov 27 14:17 postmaster.pid

With the package installation, PostgreSQL is automatically added to the OS startup list, so there is no need to start it manually. Use the following commands to control the server as a privileged OS user with sudo: Stop the server:

student$ sudo pg_ctlcluster 16 main stop

Start the server:

student$ sudo pg_ctlcluster 16 main start

Restart:

student$ sudo pg_ctlcluster 16 main restart

Reload configuration:

student$ sudo pg_ctlcluster 16 main reload

Get server information:

student$ sudo pg_ctlcluster 16 main status

pg_ctl: server is running (PID: 2836)
/usr/lib/postgresql/16/bin/postgres "-D" "/var/lib/postgresql/16/main" "-c"
"config_file=/etc/postgresql/16/main/postgresql.conf"

List of installed instances (works without sudo):

student$ pg_lsclusters

Ver Cluster Port Status Owner    Data directory              Log file
16  main    5432 online postgres /var/lib/postgresql/16/main

Page 7: Page 7

/var/log/postgresql/postgresql-16-main.log

Page 8: Server Message Log

Server message log contains

• server messages
• user session messages
• application messages
• Log configuration
  • log file location
  • message format
  • events to log

Speaker notes

Database operations are tracked in the server message log. The log keeps records about starting and stopping the server, as well as various signal messages, including messages about possible issues.

It can also store records of executed commands, their running time, locks that occur, etc. It can be used to trace user sessions.

Application developers can generate and log their own messages.

PostgreSQL allows you to flexibly configure which messages and in which format should be recorded into the log.

For example, the CSV and JSON output formats are convenient for automating log analysis.

https://postgrespro.com/docs/postgresql/16/runtime-config-logging

Page 9: Server Message Log

The server message log is located here:

student$ ls -l /var/log/postgresql/postgresql-16-main.log

-rw-r----- 1 postgres adm 4532 Nov 27 14:17 /var/log/postgresql/postgresql-16-main.log

Let’s look at the last messages:

student$ tail -n 10 /var/log/postgresql/postgresql-16-main.log

2025-11-27 14:17:36.340 MSK [812] LOG:  background worker "logical replication launcher"
(PID 837) exited with exit code 1
2025-11-27 14:17:36.344 MSK [829] LOG:  shutting down
2025-11-27 14:17:36.350 MSK [829] LOG:  checkpoint starting: shutdown immediate
2025-11-27 14:17:36.382 MSK [829] LOG:  checkpoint complete: wrote 3 buffers (0.0%); 0
WAL file(s) added, 0 removed, 0 recycled; write=0.009 s, sync=0.005 s, total=0.038 s;
sync files=2, longest=0.003 s, average=0.003 s; distance=0 kB, estimate=0 kB;
lsn=0/1963610, redo lsn=0/1963610
2025-11-27 14:17:36.391 MSK [812] LOG:  database system is shut down
2025-11-27 14:17:37.181 MSK [2836] LOG:  starting PostgreSQL 16.11 (Ubuntu
16.11-1.pgdg24.04+1) on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu
13.3.0-6ubuntu2~24.04) 13.3.0, 64-bit
2025-11-27 14:17:37.182 MSK [2836] LOG:  listening on IPv4 address "127.0.0.1", port 5432
2025-11-27 14:17:37.186 MSK [2836] LOG:  listening on Unix socket
"/var/run/postgresql/.s.PGSQL.5432"
2025-11-27 14:17:37.207 MSK [2839] LOG:  database system was shut down at 2025-11-27
13:16:17 MSK
2025-11-27 14:17:37.243 MSK [2836] LOG:  database system is ready to accept connections

Page 10: Configuration Parameters

For the entire instance

• the main configuration file is postgresql.conf

ALTER SYSTEM modifies postgresql.auto.conf

• For the current session

SET/RESET
set_config()

• View the current setting

SHOW
current_setting()
pg_settings
\dconfig

Speaker notes

The PostgreSQL server configuration is governed by a variety of parameters that are used to manage resource consumption, tune system processes and user sessions, manage the server log, and handle many other tasks. It’s important to know how to check and update the parameter values.

Server configuration is usually stored in configuration files. The main configuration file is postgresql.conf, it has to be edited manually. The second configuration file is postgresql.auto.conf. Its contents are set using the ALTER SYSTEM command. The parameters set via ALTER SYSTEM take precedence over the parameters in postgresql.conf.

File and directory inclusion directives include and include_dir allow splitting large postgresql.conf into manageable parts. This may come in handy when managing multiple servers with similar configurations.

Most configuration parameters can be adjusted within a session with no server restart. You can define custom parameters and manage them in the same manner as with the system parameters.

Different ways of setting and updating parameters are described here:

https://postgrespro.com/docs/postgresql/16/config-setting

And the current parameter values are shown in the pg_settings view.

https://postgrespro.com/docs/postgresql/16/view-pg-settings

Page 11: Configuration Parameters

The main postgresql.conf configuration file is located in this directory:

student$ ls -l /etc/postgresql/16/main

total 60
drwxr-xr-x 2 postgres postgres  4096 Nov 27 13:14 conf.d
-rw-r--r-- 1 postgres postgres   315 Nov 27 13:14 environment
-rw-r--r-- 1 postgres postgres   143 Nov 27 13:14 pg_ctl.conf
-rw-r----- 1 postgres postgres  5743 Nov 27 13:14 pg_hba.conf
-rw-r----- 1 postgres postgres  2640 Nov 27 13:14 pg_ident.conf
-rw-r--r-- 1 postgres postgres 29960 Nov 27 13:14 postgresql.conf
-rw-r--r-- 1 postgres postgres   317 Nov 27 13:14 start.conf

Other configuration files are also stored here. Let’s check the value of the work_mem parameter:

=> SHOW work_mem;

 work_mem
----------
 4MB
(1 row)

The work_mem parameter specifies the amount of memory that will be used for internal sorting and hash table allocation operations before using temporary files on disk. 4MB is the default value and it is too small. Let’s say we want to increase it to 16MB for the entire instance. There are various ways to do this. First, you can uncomment and change the line in postgresql.conf where the parameter is defined:

student$ grep '#work_mem' /etc/postgresql/16/main/postgresql.conf

#work_mem = 4MB
# min 64kB

Secondly, you can place the parameter definition in a file with the .conf suffix in the /etc/postgresql/16/main/conf.d directory or in a custom configuration file, the location of which should be set in the include directive of the main configuration file postgresql.conf. Thirdly, you can change the parameter value using an SQL command, and this is what we will do:

=> ALTER SYSTEM SET work_mem TO '16MB';

ALTER SYSTEM

This change does not end up in postgresql.conf, but in postgresql.auto.conf, which is located in the PGDATA directory:

student$ sudo cat /var/lib/postgresql/16/main/postgresql.auto.conf

# Do not edit this file manually!
# It will be overwritten by the ALTER SYSTEM command.
work_mem = '16MB'

Reload the configuration files for the change to take effect. To do this, you can use pg_ctlcluster, or use the SQL function:

=> SELECT pg_reload_conf();

 pg_reload_conf
----------------
 t
(1 row)

Verify that the new value is applied. Here is another way to check it:

=> SELECT current_setting('work_mem');

 current_setting
-----------------
 16MB
(1 row)

To restore the default value of a parameter, you can use the RESET command instead of SET (and then reload the configuration, of course):

=> ALTER SYSTEM RESET work_mem;

Page 12: Page 12

ALTER SYSTEM

=> SELECT pg_reload_conf();

 pg_reload_conf
----------------
 t
(1 row)

Most parameter values can be set for the current session live. For example, you can increase work_mem just for a single query that you expect to sort a large volume of data:

=> SET work_mem = '64MB';

SET

The new value will remain for the current session or even for the current transaction (with SET LOCAL). Yet another way to check a current value is to query the pg_settings view:

=> SELECT name, setting, unit FROM pg_settings WHERE name = 'work_mem';

   name   | setting | unit
----------+---------+------
 work_mem | 65536   | kB
(1 row)

Lastly, there is the \dconfig command:

=> \dconfig work_mem

List of configuration parameters
 Parameter | Value
-----------+-------
 work_mem  | 64MB
(1 row)

Page 13: The psql Client

Terminal client for working with PostgreSQL

• Comes with the DBMS
• Used by administrators and developers for interactive work and script execution

Speaker notes

There are other third-party tools available, but they are not considered in the scope of the course.

In the course, we will use the psql terminal client:

1. psql is the only client supplied with the DBMS.

2. The knowledge of psql will be useful to both developers and DB administrators, regardless of which tool they choose to work with at the end of the day.

For interactivity, psql provides built-in support for readline and pager programs (such as less and pspg), as well as the option to use external editing tools. Using psql, you can interact with the operating system, browse through the system catalog, and write scripts to automate routine tasks.

https://postgrespro.com/docs/postgresql/16/app-psql

Page 14: Connection

When starting psql, you need to specify the connection parameters. Required parameters include: database name, same as the user name by default user name (role), same as the OS user name by default host, local connection by default port, usually 5432 by default This is how you put them in:

student$ psql -d database -U user -h host -p port

The VM is set up to connect to PostgreSQL without specifying the parameters:

student$ psql

Check the connection:

=> \conninfo

You are connected to database "student" as user "student" via socket in
"/var/run/postgresql" at port "5432".

The \connect command creates a new connection without leaving psql. You can use its short form: \c. From here on, the optional parts of commands will be shown in square brackets: \c[onnect].

Help and Documentation

You don’t need to open the documentation every time you need to check something. Instead, you can get the information from within the system directly. The command

student$ psql --help

displays the help information for psql. If PostgreSQL was installed with documentation, then you can get the reference manual with the command

student$ man psql

psql can execute SQL commands and its own commands which start with a backslash, such as \conninfo. psql commands are always single-line, unlike SQL commands. Inside psql, you can get a list and a brief description of all psql commands: \? displays the list of psql commands \h[elp] provides a list of SQL commands that the server supports, as well as the syntax of an SQL command (if specified).

Formatting the Output

The psql client can return output in different formats: aligned format unaligned format extended format The aligned format is the default:

=> SELECT name, setting, unit FROM pg_settings LIMIT 7;

            name            |  setting   | unit
----------------------------+------------+------
 allow_in_place_tablespaces | off        |
 allow_system_table_mods    | off        |
 application_name           | psql       |
 archive_cleanup_command    |            |
 archive_command            | (disabled) |
 archive_library            |            |
 archive_mode               | off        |
(7 rows)

It sets each column’s width based on its contents. There’s also the header and the footer. psql commands to switch display modes: \a — mode switch: aligned/unaligned. \t — toggle the header and footer display. Let’s disable alignment, heading, and summary line:

=> \a \t

Output format is unaligned.
Tuples only is on.

=> SELECT name, setting, unit FROM pg_settings LIMIT 7;

Page 15: Page 15

allow_in_place_tablespaces|off|
allow_system_table_mods|off|
application_name|psql|
archive_cleanup_command||
archive_command|(disabled)|
archive_library||
archive_mode|off|

=> \a \t

Output format is aligned.
Tuples only is off.

This format is not the best for readability, but can be more suitable for automatic processing. The extended format is best for displaying multiple columns for one or several records. It is switched on for the current command with the \gx flag at the end in place of a semicolon:

=> SELECT name, setting, unit, category, context, vartype,
    min_val, max_val, boot_val, reset_val
FROM pg_settings
WHERE name = 'work_mem' \gx

-[ RECORD 1 ]----------------------
name      | work_mem
setting   | 4096
unit      | kB
category  | Resource Usage / Memory
context   | user
vartype   | integer
min_val   | 64
max_val   | 2147483647
boot_val  | 4096
reset_val | 4096

Or you can toggle it on and off with the \x flag. The \pset command displays all formatting options.

Interacting with the OS and Executing Scripts

psql can run shell commands:

=> \! pwd

/home/student

An SQL query can generate several other SQL queries and write them to a file using the \o[ut] command:

=> \a \t \pset fieldsep ''

Output format is unaligned.
Tuples only is on.
Field separator is "".

=> \o dev1_tools.sql

=> SELECT format('SELECT %L AS tbl, count(*) FROM %I;', tablename, tablename)
FROM pg_tables LIMIT 3;

Nothing is printed to the screen (to the standard output). Check the file:

=> \! cat dev1_tools.sql

SELECT 'pg_statistic' AS tbl, count(*) FROM pg_statistic;
SELECT 'pg_type' AS tbl, count(*) FROM pg_type;
SELECT 'pg_foreign_table' AS tbl, count(*) FROM pg_foreign_table;

Revert to default output and formatting.

=> \o \t \a

Tuples only is off.
Output format is aligned.

We can run the commands from the file using \i[nclude]:

=> \i dev1_tools.sql

     tbl      | count
--------------+-------
 pg_statistic |   409
(1 row)

   tbl   | count
---------+-------
 pg_type |   613
(1 row)

       tbl        | count
------------------+-------
 pg_foreign_table |     0
(1 row)

There are other ways to execute commands, including from files. After executing the commands, the psql session will be terminated: psql < filename psql -f < filename psql -c ‘command’ (one command per call)

Page 16: psql Variables

Like shell, psql has its own variables. Set a variable:

=> \set TEST Hi!

To replace a variable with its value, use the colon in front of its name:

=> \echo :TEST

Hi!

Unset a value:

=> \unset TEST

=> \echo :TEST

:TEST

Variables can be used, for example, to store the text of frequently used queries. Here is a query that returns a list of the five largest tables:

=> \set top5 'SELECT tablename, pg_total_relation_size(schemaname||''.''||tablename) AS bytes FROM pg_tables ORDER BY bytes DESC LIMIT 5;'

Now we can execute the query by just typing:

=> :top5

   tablename    |  bytes
----------------+---------
 pg_proc        | 1245184
 pg_rewrite     |  745472
 pg_attribute   |  720896
 pg_description |  630784
 pg_statistic   |  294912
(5 rows)

You can add the command to set the value of top5 to the .psqlrc starter file in the user’s home directory. Commands from .psqlrc are executed automatically every time psql starts. If used with no parameters, \set displays all currently set variables and their values, including the built-in ones. You can check the help for the built-in variables:

\? variables

To exit psql, either use \q[uit], quit, or exit, or press Ctrl+D:

=> \q

Page 17: Takeaways

Installing PostgreSQL from pre-built packages is the preferred installation type

• Pre-packaged distributions bring some OS specifics that you should be aware of:
  • how to start and stop the server
  • location of configuration files
  • location of the server message log
• psql is a client application for working with PostgreSQL

Page 18: Practice

1. Set the parameter work_mem to 8MB for all sessions. Reload the configuration and verify that the changes have taken effect. Restore the default value. 2. Put the command to create a table to the ddl.sql file. Put the commands to insert rows into this table to the populate.sql file. Run both scripts and verify that the table has been created and populated. 3. Find today’s records in the server message log.

Speaker notes

To launch psql in the terminal window, type psql without parameters.

student:~$ psql

It is convenient to have separate databases for tasks that are related to different topics:

student/student=# CREATE DATABASE tools_overview;

CREATE DATABASE

student/student=# \c tools_overview
You are now connected to database "tools_overview" as user
"student".
student/tools_overview=#

1. Use the ALTER SYSTEM command.

2. If the output does not fit into one terminal screen, psql forwards it to the tool called less for page-by-page output. To return to the prompt, press q.

Page 19: 1. Configuration Parameters

Connect to the database:

student$ psql

Set the parameters:

=> ALTER SYSTEM SET work_mem = '8MB';

ALTER SYSTEM

Reload the configuration:

=> SELECT pg_reload_conf();

 pg_reload_conf
----------------
 t
(1 row)

Check the parameter value:

=> \dconfig work_mem

List of configuration parameters
 Parameter | Value
-----------+-------
 work_mem  | 8MB
(1 row)

Reset to the default value:

=> ALTER SYSTEM RESET work_mem;

ALTER SYSTEM

Apply changes:

=> SELECT pg_reload_conf();

 pg_reload_conf
----------------
 t
(1 row)

2. Executing Scripts in psql

Write a command into ’ddl.sql’ to create a table in PostgreSQL (you can use any text editor):

student$ cat > ~/ddl.sql <<EOF
CREATE TABLE keywords (
    word text,
    category text,
    description text
);
EOF

Write commands into ’populate.sql’ to populate the table:

student$ cat > ~/populate.sql <<EOF
INSERT INTO keywords
  SELECT word, catcode, catdesc FROM pg_get_keywords();
EOF

Create a new database and connect to it:

=> CREATE DATABASE tools_overview;

CREATE DATABASE

=> \c tools_overview

You are now connected to database "tools_overview" as user "student".

Run the scripts and check the records in the table:

Page 20: Page 20

=> \i ddl.sql

CREATE TABLE

=> \i populate.sql

INSERT 0 471

=> SELECT * FROM keywords LIMIT 10;

   word    | category | description
-----------+----------+-------------
 abort     | U        | unreserved
 absent    | U        | unreserved
 absolute  | U        | unreserved
 access    | U        | unreserved
 action    | U        | unreserved
 add       | U        | unreserved
 admin     | U        | unreserved
 after     | U        | unreserved
 aggregate | U        | unreserved
 all       | R        | reserved
(10 rows)

3. Viewing the Log

The log can be viewed in any text editor. Each log record starts with a date, contains the server process ID (with the packaged installation configuration), and may span several lines. The last records will be at the end of the file.

student$ tail /var/log/postgresql/postgresql-16-main.log

2025-11-27 14:26:39.316 MSK [44254] LOG:  database system is shut down
2025-11-27 14:26:40.321 MSK [46618] LOG:  starting PostgreSQL 16.11 (Ubuntu
16.11-1.pgdg24.04+1) on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu
13.3.0-6ubuntu2~24.04) 13.3.0, 64-bit
2025-11-27 14:26:40.321 MSK [46618] LOG:  listening on IPv4 address "127.0.0.1", port 5432
2025-11-27 14:26:40.325 MSK [46618] LOG:  listening on Unix socket
"/var/run/postgresql/.s.PGSQL.5432"
2025-11-27 14:26:40.341 MSK [46621] LOG:  database system was shut down at 2025-11-27
13:16:17 MSK
2025-11-27 14:26:40.367 MSK [46618] LOG:  database system is ready to accept connections
2025-11-27 14:26:43.184 MSK [46618] LOG:  received SIGHUP, reloading configuration files
2025-11-27 14:26:43.185 MSK [46618] LOG:  parameter "work_mem" changed to "8MB"
2025-11-27 14:26:43.572 MSK [46618] LOG:  received SIGHUP, reloading configuration files
2025-11-27 14:26:43.572 MSK [46618] LOG:  parameter "work_mem" removed from configuration
file, reset to default

The database can now be disconnected and deleted (see the Data Organization module for more)

=> \c postgres

You are now connected to database "postgres" as user "student".

=> DROP DATABASE tools_overview;

DROP DATABASE