PostgreSQL

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This document describes how to set up PostgreSQL. It also describes how to configure PostgreSQL to be accessible from a remote client. If you need help setting up the rest of a web stack, see the LAMP page and follow all of the sections except the one related to MySQL.

Several sections have instructions stating "become the postgres user". If sudo is installed, execute the following to get a shell as the postgres user:

sudo -i -u postgres

Otherwise su can be used:

su root
su - postgres

Installing PostgreSQL

  • Install postgresql
# pacman -S postgresql
  • Start the PostgreSQL server (The first time that this is run it will create the data directory and users needed to run the server. As such you will see a lot of output.)
# rc.d start postgresql
  • (Optional) Add postgresql to the list of daemons that start on system startup in the /etc/rc.conf file

Creating Your First Database/User

  • Become the postgres user. Add a new database user using the createuser command.

If you create a user as per your login user ($USER) it allows you to access the postgresql database shell without having to specify a user to login (which makes it quite convenient).

e.g. to create a superuser

 $ createuser -s -U postgres
 $ Enter name of role to add: myUsualArchLoginName
  • Create a new database over which the above user has read/write privileges using the createdb command.

From your login shell (not the postrgres user's)

 $ createdb

Familiarizing Yourself with PostgreSQL

Access the database shell

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

Some helpful commands:

  • Connect to a particular database
=> \c <database>
  • List all users and their permission levels
=> \du
  • Shows summary information about all tables in the current database
=> \dt
  • exit/quit the psql shell
=> \q or CTRL+d

There are of course many more meta-commands, but these should help you get started.

Configure PostgreSQL to be accessible from remote hosts

The PostgreSQL database server configuration file is postgresql.conf. This file is located in the data directory of the server, typically /var/lib/postgres/data. This folder also houses the other main config files, including the pg_hba.conf.

Note: By default this folder will not even be browseable (or searchable) by a regular user, if you are wondering why `find` or `locate` is not finding the conf files, this is the reason (threw me for a loop the first time I installed).
  1. As root user edit the file
    # vim /var/lib/postgres/data/postgresql.conf
  2. In the connections and authentications section uncomment or edit the listen_addresses line to your needs
    listen_addresses = '*'
    and take a careful look at the other lines.
  3. Hereafter insert the following line in the host-based authentication file /var/lib/postgres/data/pg_hba.conf. This file controls which hosts are allowed to connect, so be careful.
# IPv4 local connections:
host   all   all   your_desired_ip_address/32   trust

where your_desired_ip_address is the IP address of the client.

  1. After this you should restart the daemon process for the changes to take effect with
    # rc.d restart postgresql
Note: Postgresql uses port 5432 by default for remote connections. So make sure this port is open and able to receive incoming connections

For troubleshooting take a look in the server log file

tail /var/log/postgresql.log

Configure PostgreSQL to Work With PHP

  1. Install the PHP-PostgreSQL modules
    # pacman -S php-pgsql 
  2. Open the file /etc/php/php.ini with your editor of choice, e.g.,
    # vim /etc/php/php.ini
  3. Find the line that starts with, ";extension=pgsql.so" and change it to, "extension=pgsql.so". (Just remove the preceding ";"). If you need PDO, do the same thing with ";extension=pdo.so" and ";extension=pdo_pgsql.so". If these lines are not present, add them. These lines may be in the "Dynamic Extensions" section of the file, or toward the very end of the file.
  4. Restart the Apache web server
    # rc.d restart httpd

Change Default Data Dir (Optional)

By default, when installing PostgreSQL the directory were all your newly created databases will be stored is /var/lib/postgres/data. If you want to change this behavior, you have to follow these steps:

  1. Create the new directory and assign it to user postgres (you eventually have to become root):
# mkdir /mypath/mydatadir
# chown postgres:postgres /mypath/mydatadir
  1. Become the postgres user, and initialize the new cluster:
$ initdb -D /mypath/mydatadir
  1. Edit /etc/conf.d/postgresql and change the PGROOT variable to point at your new data directory.

Change Default Encoding of New Databases To UTF-8 (Optional)

When creating a new database (e.g. with createdb blog) PostgreSQL actually copies a template database. There are two predefined templates: template0 is vanilla, while template1 is meant as an on-site template changeable by the administrator and is used by default. In order to change the encoding of new database, one of the options is to change on-site template1. To do this, log into PostgresSQL shell (psql) and execute the following:

1. First, we need to drop template1. Templates cannot be dropped, so we first modify it so it is an ordinary database:

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

2. Now we can drop it:

DROP DATABASE template1;

3. The next step is to create a new database from template0, with a new default encoding:

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

4. Now modify template1 so it is actually a template:

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

6. (OPTIONAL) If you do not want anyone connecting to this template, set datallowconn to FALSE:

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

Now you can create a new database by running from regular shell:

su -
su - postgres
createdb blog;

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

\l

returns

                              List of databases
  Name    |  Owner   | Encoding  | Collation | Ctype |   Access privileges
-----------+----------+-----------+-----------+-------+----------------------
blog      | postgres | UTF8      | C         | C     |
postgres  | postgres | SQL_ASCII | C         | C     |
template0 | postgres | SQL_ASCII | C         | C     | =c/postgres
                                                     : postgres=CTc/postgres
template1 | postgres | UTF8      | C         | C     |

Installing phpPgAdmin (optional)

phpPgAdmin is a web-based administration tool for PostgreSQL.

  1. Make sure that the [community] repo is enabled.
  2. Install the package via Pacman
    # pacman -S phppgadmin

Installing pgAdmin (optional)

pgAdmin is a GUI-based administration tool for PostgreSQL.

  1. Install the package via Pacman
    # pacman -S pgadmin3

Upgrading PostgreSQL

Warning: Official PostgreSQL upgrade documentation should be followed.

Note that these instructions could cause data loss. Use at your own risk.

It is recommended to add the following to your /etc/pacman.conf file:

IgnorePkg = postgresql postgresql-libs

This will ensure you do not accidentally upgrade the database to an incompatible version. When an upgrade is available, pacman will notify you that it is skipping the upgrade because of the entry in pacman.conf. Minor version upgrades (e.g., 9.0.3 to 9.0.4) are safe to perform. However, if you do an accidental upgrade to a different major version (e.g., 9.0.X to 9.1.X), you might not be able to access any of your data. Always check the PostgreSQL home page (http://www.postgresql.org/) 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.

For those wishing to use pg_upgrade, a Template:Package Official package is available in the repositories 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. When you are ready to perform the upgrade, you can do

pacman -Syu postgresql postgresql-libs postgresql-old-upgrade

Note also that the data directory does not change from version to version, so before running pg_upgrade it is necessary to rename your existing data directory and migrate into a new directory. The new database must be initialized by starting the server, as described near the top of this page. The server then needs to be stopped before running pg_upgrade.

# rc.d stop postgresql
# su - postgres -c 'mv /var/lib/postgres/data /var/lib/postgres/olddata'
# rc.d start postgresql
# rc.d stop postgresql

Reference the upstream pg_upgrade documentation for details.

The upgrade invocation will likely look something like the following (run as the postgres user). Do not run this command blindly without understanding what it does!

# pg_upgrade -d /var/lib/postgres/olddata/ -D /var/lib/postgres/data/ -b /opt/pgsql-8.4/bin/ -B /usr/bin/

You could also do something like this (after the upgrade and install of postgresql-old-upgrade)

# rc.d stop postgresql
# /opt/pgsql-8.4/bin/pg_ctl -D /var/lib/postgres/olddata/ start
# pg_dumpall >> old_backup.sql
# /opt/pgsql-8.4/bin/pg_ctl -D /var/lib/postgres/olddata/ stop
# rc.d start postgresql
# psql -f old_backup.sql postgres

Performance issues

If you're using PostgresSQL on a local machine for development and it seems slow, you could try turning fsync off in the configuration (/var/lib/postgres/data/postgresql.conf).

fsync = off

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