PostgreSQL

PostgreSQL is an open source, community driven, standard compliant object-relational database system.

Installation

Warning: See #Upgrading PostgreSQL for necessary steps before installing new versions of the PostgreSQL packages.

Install the postgresql package. It will also create a system user called postgres.

You can now switch to the postgres user using a privilege elevation program.

Note: Commands that should be run as the postgres user are prefixed by [postgres]$ in this article.

You can switch to the PostgreSQL user by executing the following command:

• If you have sudo and are in sudoers:

  $ sudo -iu postgres

• Otherwise using su:

  $ su
  # su -l postgres
  

See sudo(8) or su(1) for their usage.

Initial configuration

Before PostgreSQL can function correctly, the database cluster must be initialized:

[postgres]$ initdb -D /var/lib/postgres/data

Where -D is the default location where the database cluster must be stored (see #Change default data directory if you want to use a different one). accepts a number of extra arguments:

• By default, the locale and the encoding for the database cluster are derived from your current environment (using $LANG value). If this is not what you want, you can override the defaults using (where locale is to be chosen amongst the system's available locales) and (which must match the chosen locale). (Once the database is up, you can check which values were used with .)
• If your data directory resides on a file system without data checksumming, you may wish to enable PostgreSQL's built-in checksumming for increased integrity guarantees - add the --data-checksums argument to do so. Read #Enable data checksumming for more information. (Once the database is up, you can check if it is enabled with .)
• For more options, see and official documentation.

Example:

[postgres]$ initdb --locale=C.UTF-8 --encoding=UTF8 -D /var/lib/postgres/data --data-checksums

Many lines should now appear on the screen with several ending by :

If these are the kind of lines you see, then the process succeeded. Return to the regular user using .

Note: To read more about this WARNING, see #Restricts access rights to the database superuser by default.

Finally, start and enable the .

Create your first database/user

Tip: If you create a PostgreSQL role/user with the same name as your Linux username, it allows you to access the PostgreSQL database shell without having to specify a user to login (which makes it quite convenient).

Become the postgres user. Add a new database role/user using the createuser command:

[postgres]$ createuser --interactive

Create a new database over which the above user has read/write privileges using the createdb command (execute this command from your login shell if the database user has the same name as your Linux user, otherwise add to the following command):

$ createdb myDatabaseName

Familiarize with PostgreSQL

Access the database shell

Become the postgres user. Start the primary database shell, psql, where you can do all your creation of databases/tables, deletion, set permissions, and run raw SQL commands. Use the option to connect to the database you created (without specifying a database, will try to access a database that matches your username).

[postgres]$ psql -d myDatabaseName

Some helpful commands:

Get help:

=> \help

Connect to a particular database:

=> \c <database>

List all users and their permission levels:

=> \du

Show summary information about all tables in the current database:

=> \dt

Exit/quit the shell:

=> \q or CTRL+d

There are of course many more meta-commands, but these should help you get started. To see all meta-commands run:

=> \?

Optional configuration

The PostgreSQL database server configuration file is . This file is located in the data directory of the server, typically . This folder also houses the other main configuration files, including the which defines authentication settings, for both local users and other hosts ones.

Restricts access rights to the database superuser by default

The defaults allow any local user to connect as any database user, including the database superuser. This is likely not what you want, so in order to restrict global access to the postgres user, change the following line:

/var/lib/postgres/data/pg_hba.conf

# TYPE  DATABASE        USER            ADDRESS                 METHOD

# "local" is for Unix domain socket connections only
local   all             all                                     trust

To:

/var/lib/postgres/data/pg_hba.conf

# TYPE  DATABASE        USER            ADDRESS                 METHOD

# "local" is for Unix domain socket connections only
local   all             postgres                                peer

You might later add additional lines depending on your needs or software ones.

Require password for login

Edit and set the authentication method for each user (or "all" to affect all users) to (preferred), or (less secure; should be avoided if possible):

If you choose , you must also edit and set:

Restart , and then re-add each user's password using .

Configure PostgreSQL to be accessible exclusively through UNIX Sockets

In the connections and authentications section of your configuration, set:

This will disable network listening completely. After this you should restart for the changes to take effect.

Configure PostgreSQL to be accessible from remote hosts

In the connections and authentications section, set the listen_addresses line to your needs:

You can use '*' to listen on all available addresses.

Then add a line like the following to the authentication config:

where is the IP address of the remote client.

See the documentation for pg_hba.conf.

After this you should restart for the changes to take effect.

For troubleshooting take a look in the server log file:

# journalctl -u postgresql.service

Configure PostgreSQL authenticate against PAM

PostgreSQL offers a number of authentication methods. If you would like to allow users to authenticate with their system password, additional steps are necessary. First you need to enable PAM for the connection.

For example, the same configuration as above, but with PAM enabled:

The PostgreSQL server is however running without root privileges and will not be able to access . We can work around that by allowing the postgres group to access this file:

# setfacl -m g:postgres:r /etc/shadow

Change default data directory

The default directory where all your newly created databases will be stored is . To change this, follow these steps:

Create the new directory and make the postgres user its owner:

# mkdir -p /pathto/pgroot/data
# chown -R postgres:postgres /pathto/pgroot

Become the postgres user, and initialize the new cluster:

[postgres]$ initdb -D /pathto/pgroot/data

Edit to create a drop-in file and override the and settings. For example:

/etc/systemd/system/postgresql.service.d/PGROOT.conf

[Service]
Environment=PGROOT=''/pathto/pgroot''
PIDFile=''/pathto/pgroot/''data/postmaster.pid

If you want to use /home directory for default directory or for tablespaces, add one more line in this file:

ProtectHome=false

Change default encoding of new databases to UTF-8

When creating a new database (e.g. with ) PostgreSQL actually copies a template database. There are two predefined templates: is vanilla, while is meant as an on-site template changeable by the administrator and is used by default. In order to change the encoding of a new database, one of the options is to change on-site . To do this, log into PostgreSQL shell () and execute the following:

First, we need to drop . Templates cannot be dropped, so we first modify it so it is an ordinary database:

UPDATE pg_database SET datistemplate = FALSE WHERE datname = 'template1';

Now we can drop it:

DROP DATABASE template1;

The next step is to create a new database from , with a new default encoding:

CREATE DATABASE template1 WITH TEMPLATE = template0 ENCODING = 'UNICODE';

Now modify so it is actually a template:

UPDATE pg_database SET datistemplate = TRUE WHERE datname = 'template1';

Optionally, if you do not want anyone connecting to this template, set to :

UPDATE pg_database SET datallowconn = FALSE WHERE datname = 'template1';

Now you can create a new database:

[postgres]$ createdb blog

If you log back in to and check the databases, you should see the proper encoding of your new database:

Enable data checksumming

If your database files reside on a file system without checksumming, its data is suspectible to silent data corruption due to bit rot and broken hardware. While those events are rare, you might want to enable PostgreSQL's built-in data checksumming if you care about data integrity. This feature must be enabled on the cluster level, not per-database or per-table.

Note: This feature has a number of caveats:

• There is a minimal performance impact, especially while reading large datasets from disk. In-memory operations are not affected.
• PostgreSQL is unable to repair corrupt data - it will only abort transactions reading from corrupt pages to prevent further damage or invalid execution results.
• Checksums cover on-disk data (row) pages only, not metadata or control structures. In-memory pages are not checksummed. Error-corrected storage and ECC memory is still beneficial.

• To enable checksumming during cluster creation, add the --data-checksums argument to .
• To verify whenever checksumming is enabled, run (which should print or on).
• To toggle checksumming on an existing cluster:

1. Stop .
2. Run (or if you no longer want checksumming). Enabling checksums will rewrite all database pages, which will take a while for large database instances.
3. Start .

Graphical tools

For tools supporting multiple DBMSs, see List of applications/Documents#Database tools.

Upgrading PostgreSQL

Upgrading major PostgreSQL versions (e.g. version 13.x to version 14.y) requires some extra maintenance.

Note: Official PostgreSQL upgrade documentation should be followed.

Get the currently used database version via

# cat /var/lib/postgres/data/PG_VERSION

To ensure you do not accidentally upgrade the database to an incompatible version, it is recommended to skip updates to the PostgreSQL packages.

Minor version upgrades are safe to perform. However, if you do an accidental upgrade to a different major version, you might not be able to access any of your data. Always check the PostgreSQL home page to be sure of what steps are required for each upgrade. For a bit about why this is the case, see the versioning policy.

There are two main ways to upgrade your PostgreSQL database. Read the official documentation for details.

pg_upgrade

The utility attempts to copy over as much compatible data as possible between clusters and upgrading everything else. It is generally the fastest method to upgrade most instances, although it requires access to binaries for both source and target PostgreSQL versions. Read the man page to understand what actions it performs. For non-trivial instances (e.g. with streaming replication or log-shipping), read the upstream documentation first.

For those wishing to use , a package is available that will always run one major version behind the real PostgreSQL package. This can be installed side-by-side with the new version of PostgreSQL. To upgrade from older versions of PostgreSQL there are AUR packages available, e.g. . (You must use the version packaged with the PostgreSQL version you are upgrading to.)

Note that the database cluster directory does not change from version to version, so before running , it is necessary to rename your existing data directory and migrate into a new directory. The new database cluster must be initialized using the same parameters as the old one.

When you are ready to begin the upgrade:

1. While the old database cluster is still online, collect the arguments used to create it. Refer to #Initial configuration for more information.
2. Stop . (Check the unit status to be sure that PostgresSQL was stopped correctly. If it failed, will fail too.)
3. Upgrade postgresql, , and .
4. Rename the old cluster directory, then create a new cluster and temporary working directory:
5. Initialize the new cluster using the same arguments as were used for the old cluster:
6. Upgrade the cluster, replacing PG_VERSION below, with the old PostgreSQL version number (e.g. 13):
7. Start again.
8. Optional: Run to recalculate query analyzer statistics, which should improve query performance shortly after the upgrade. (Adding argument may improve this command's performance.)
9. Optional: Back up the directory in case you need to restore a previous PostgreSQL version.
10. Delete the directory with old cluster data.
11. Delete the directory.

Manual dump and reload

You could also do something like this (after the upgrade and install of ).

Stop

# mv /var/lib/postgres/data /var/lib/postgres/olddata
# mkdir /var/lib/postgres/data
# chown postgres:postgres /var/lib/postgres/data
[postgres]$ initdb -D /var/lib/postgres/data
[postgres]$ /opt/pgsql-13/bin/pg_ctl -D /var/lib/postgres/olddata/ start
# cp /usr/lib/postgresql/postgis-3.so /opt/pgsql-13/lib/ # Only if postgis installed
[postgres]$ pg_dumpall -h /tmp -f /tmp/old_backup.sql
[postgres]$ /opt/pgsql-13/bin/pg_ctl -D /var/lib/postgres/olddata/ stop

Start

[postgres]$ psql -f /tmp/old_backup.sql postgres

Troubleshooting

Improve performance of small transactions

If you are using PostgresSQL on a local machine for development and it seems slow, you could try turning synchronous_commit off in the configuration. Beware of the caveats, however.

Prevent disk writes when idle

PostgreSQL periodically updates its internal "statistics" file. By default, this file is stored on disk, which prevents disks from spinning down on laptops and causes hard drive seek noise. It is simple and safe to relocate this file to a memory-only file system with the following configuration option:

/var/lib/postgres/data/postgresql.conf

stats_temp_directory = '/run/postgresql'

pgAdmin 4 issues after upgrade to PostgreSQL 12

If you see errors about string indices must be integers when navigating the tree on the left, or about when viewing the data, remove the server from the connection list in pgAdmin and add a fresh server instance. pgAdmin will otherwise continue to treat the server as a PostgreSQL 11 server resulting in these issues.

PostgreSQL database unable to start after package update when using extensions

The cause in this case is mostly the existing package is not compiled for the newer version (and it may be up-to-date), the solution is rebuilding the package either manually or waiting for an update to the extension package.

Failing to start a PostgreSQL server with the older version of the database while upgrading to the newer version with extensions

This is caused because the old version of postgres from the package does not have the required extensions (.so files) in its lib directory, the current solution is dirty, and might cause a lot of problems so keep a backup of the database just in case, basically copy the required extension .so files from to (remember to replace XX with the major version of ).

For example, for timescaledb

# cp /usr/lib/postgresql/timescaledb*.so /opt/pgsql-13/lib/

to know the exact files to copy, check the contant of the package of the extension using :

$ pacman -Ql package_name