= PostgreSQL

[[installation]]
== Installation

The installation and initialization of the postgresql server is a little
bit different in comparison to other packages and other linux distros.
This document aims to summarize basic installation steps relevant to
recent fedora release. In the first place, you may consider installing a newer
version than is packaged for Fedora, see https://yum.postgresql.org/[1].
However, this is not recommended.

....
sudo yum install postgresql-server postgresql-contrib
....

Or with dnf in Fedora 22 and later versions:

....
sudo dnf install postgresql-server postgresql-contrib
....

The postgresql server is turned off and disabled by default. You can
enable its start during the boot using following command:

....
sudo systemctl enable postgresql
....

You can start the postgresql server only when necessary as follows.

....
sudo systemctl start postgresql 
Job for postgresql.service failed. See 'systemctl status postgresql.service' and 'journalctl -xn' for details.
....

The database needs to be populated with initial data after installation.
The error log describes the problem and its solution.

....
journalctl -xn
-- Logs begin at Mon 2013-11-04 14:38:33 CET, end at Thu 2013-11-14 11:45:56 CET. --
Nov 14 11:45:34 mlich-lenovo.usersys.redhat.com sudo[2054]: jmlich : TTY=pts/2 ; PWD=/home/jmlich ; USER=root ; COMMAND=/bin/systemctl status postgresql
Nov 14 11:45:37 mlich-lenovo.usersys.redhat.com sudo[2073]: jmlich : TTY=pts/2 ; PWD=/home/jmlich ; USER=root ; COMMAND=/bin/systemctl status postgresql
Nov 14 11:45:56 mlich-lenovo.usersys.redhat.com sudo[2105]: jmlich : TTY=pts/2 ; PWD=/home/jmlich ; USER=root ; COMMAND=/bin/systemctl start postgresql
Nov 14 11:45:56 mlich-lenovo.usersys.redhat.com systemd[1]: Starting PostgreSQL database server...
-- Subject: Unit postgresql.service has begun with start-up
-- Defined-By: systemd
- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit postgresql.service has begun starting up.
Nov 14 11:45:56 mlich-lenovo.usersys.redhat.com postgresql-check-db-dir[2108]: An old version of the database format was found.
Nov 14 11:45:56 mlich-lenovo.usersys.redhat.com postgresql-check-db-dir[2108]: Use "postgresql-setup upgrade" to upgrade to version 9.3.
Nov 14 11:45:56 mlich-lenovo.usersys.redhat.com postgresql-check-db-dir[2108]: See /usr/share/doc/postgresql/README.rpm-dist for more information.
Nov 14 11:45:56 mlich-lenovo.usersys.redhat.com systemd[1]: postgresql.service: control process exited, code=exited status=1
Nov 14 11:45:56 mlich-lenovo.usersys.redhat.com systemd[1]: Failed to start PostgreSQL database server.
-- Subject: Unit postgresql.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- Documentation: `http://www.freedesktop.org/wiki/Software/systemd/catalog/be02cf6855d2428ba40df7e9d022f03d
--
-- Unit postgresql.service has failed.
--
-- The result is failed.
....

The database initialization could be done using following command. It
creates the configuration files postgresql.conf and pg_hba.conf

....
sudo postgresql-setup initdb
....

Or on Fedora 22 and later:

....
sudo postgresql-setup --initdb --unit postgresql
....

[[upgrade]]
== Upgrade

As you can see from the error message in my example, it is not a fresh
installation, but an ugprade.

....
Nov 14 11:45:56 mlich-lenovo.usersys.redhat.com postgresql-check-db-dir[2108]: An old version of the database format was found.
Nov 14 11:45:56 mlich-lenovo.usersys.redhat.com postgresql-check-db-dir[2108]: Use "postgresql-setup upgrade" to upgrade to version 9.3.
....

With version 9 you can use the upgrade tool. It is packaged as
`postgresql-upgrade`:

....
postgresql-setup upgrade

Redirecting to /bin/systemctl stop  postgresql.service
Upgrading database: OK

The configuration files was replaced by default configuration.
The previous configuration and data are stored in folder /var/lib/pgsql/data-old.

See /var/lib/pgsql/pgupgrade.log for details.
....

The data are located at

* /var/lib/pgsql/data
* /var/lib/pgsql/data-old

The upgrade itself will backup your existing data and migrate your
database. Don't forget to migrate your configuration (with meld, for
example: `meld /var/lib/pgsql/data{,-old}/postgresql.conf`).

You may need to switch postgresql to trust mode before updating. This
should be fixed already.

You can also upgrade by dumping your database and loading it again. For
more information, see the link:#link-upgrade[official documentation].

[[firewall]]
== Firewall

PostgreSQL operates on port 5432 (or whatever else you set in your
`postgresql.conf`). In firewalld you can open it like this:

....
# make it last after reboot
firewall-cmd --permanent --add-port=5432/tcp
# change runtime configuration
firewall-cmd --add-port=5432/tcp
....

In the case of iptables:

....
iptables -A INPUT -p tcp --dport 5432 -m state --state NEW,ESTABLISHED -j ACCEPT
....

Bear in mind that you probably don't want to open your database server
to the whole world.

[[selinux]]
== SELinux

If you have SELinux enforced, you may run into trouble when trying to do
some non-standard configuration. For example, if you would like to change
a location of your database, you have to add new context mapping for the
new location:

....
semanage fcontext -a -t postgresql_db_t "/my/new/location(/.*)?"
....

If the default port doesn't work for you, you may need to map postgre's port type to your desired port:

....
semanage port -a -t postgresql_port_t -p tcp 5433
....

If you install a webapp that wants to communicate with PostgreSQL via
TCP/IP, you will have to tell SELinux to allow this on the webserver
host:

....
setsebool -P httpd_can_network_connect_db on
....

[[user-creation-and-database-creation]]
== User Creation and Database Creation

Eventually, you need to create a user (and database for the user).
First, you have to switch the user to interact with `postgres`:

....
su - postgres
....

and then run postgre's interactive shell:

....
psql
psql (9.3.2)
Type "help" for help.

postgres=#
....

From there you can run user creation commands:

....
postgres=# CREATE USER lenny WITH PASSWORD 'leonard';
postgres=# CREATE DATABASE carl OWNER lenny;
....

You can do this from the system shell as well:

....
createuser lenny
createdb --owner=lenny carl
....

It might be good idea to add password for the `postgres` user:

....
postgres=# \password postgres
....

[[configuration]]
== Configuration

The postgresql server is using two main configuration files

* /var/lib/pgsql/data/postgresql.conf
* /var/lib/pgsql/data/pg_hba.conf

[[systemd]]
=== systemd

Some configuration parameters are passed to daemon via command line
options. This behaviour may override settings in `postgresql.conf`. For
example, if you want to change the server's port number to 5433, create
a file named `/etc/systemd/system/postgresql.service` containing:

....
.include /lib/systemd/system/postgresql.service
[Service]
Environment=PGPORT=5433
....

Note: changing PGPORT or PGDATA will typically require adjusting SELinux
configuration as well; see section selinux.

Please follow the systemd documentation
http://fedoraproject.org/wiki/systemd#How_do_I_customize_a_unit_file.2F_add_a_custom_unit_file.3F[2]
for more details.

[[postgresql.conf]]
=== postgresql.conf

If you want postgres to accept network connections, you should change

....
listen_addresses = 'localhost'
....

to

....
listen_addresses = '*'
....

[[pg_hba.conf]]
=== pg_hba.conf

Once your database is set up, you need to configure access to your
database server. This may be done by editing file
`/var/lib/pgsql/data/pg_hba.conf`. There are rules like this in the
file:

....
# TYPE    DATABASE        USER            ADDRESS                 METHOD
  host    all             all             127.0.0.1/32            md5
  host    all             all             ::1/128                 md5
  local   all             postgres                                peer
....

First field stands for connection type. It can have these values:

* *local* — Unix-domain socket
* *host* — plain or SSL-encrypted TCP/IP socket
* *hostssl* — an SSL-encrypted TCP/IP socket
* *hostnossl* — plain TCP/IP socket

Last column specifies which authentication method will be used.

* *md5* — client has to supply password processed with MD5 algorithm
* *ident* — obtain user name of connecting client from operating system
  and consult it with specified map
* *trust* — anyone who is able to connect to PostgreSQL server may act
  as any user without supplying password
* *peer* — obtains user's name from operating system and checks if it
  matches database user name

When the database server is authenticating the client, it seeks for a record with a matching connection type, client address, requested database, and user name. As soon as it finds these credentials, it performs the authentication. If the authentication fails, no more subsequent records are taken into account. If no record matches, the client's access is denied.

The default settings are usually restricted to localhost.

When you install your database server and at first you try to "make it
work", you should turn off firewall, SELinux and make the `postgres`
authentication permissive. _Bear in mind this will greatly expose your
server, so do it [.underline]#only# on a trusted network — preferably with no network at all_:

....
host    all             all             127.0.0.1/32            trust
....

As soon as you are able to connect, turn on the security systems one by
one while verifying the connection can be established.

For more information see official documentation for
link:#link-pghba[pg_hba.conf file].

[[optimization]]
== Optimization

The default configuration of postgres is severely undertuned. It can handle simple applications without consistent database access, but if you require higher performance, you should re-configure your instance. All the magic is happening in `/var/lib/pgsql/data/postgresql.conf\``. Also, the logging mechanism is not configured very intuitively.

[[performance]]
=== Performance

The number of clients which may be connected to PostgreSQL at the same time:

....
max_connections = <number>
....

`shared_buffers` is the entry point. This is telling PostgreSQL how much
memory is dedicated for caching. Setting this to 25% of total memory of
your system is a good start. If it doesn't work for you, try to go for
something between 15% - 40% of total memory.

....
shared_buffers = <memory unit>
....

This value is used by the query planner to know how much memory is available in the system. The query planner uses this information to figure out whether the plan fits into memory or not. Setting this to 50% of total memory is a common practice.

....
effective_cache_size = <memory unit>
....

When PostgreSQL performs sorting operations, it plans its strategy
whether to sort the query on disk or in memory. Bear in mind that this
memory is available for every sorting instance. In case of multiple
users submitting queries to your database server, this can ramp up
pretty high. Therefore this is tightly bound to `max_connections`.

....
work_mem = <memory unit>
....

For more information about this topic I advise you to read the
link:#link-tuning[official documentation] about tuning PostgreSQL.

[[logging]]
=== Logging

By default, logs are rotated every week and you might not find much
information in there. One could miss a log level, date, time, etc. Also,
for simple web applications, some prefer to increase verbosity.

....
log_destination = 'stderr'
....

This is just fine. If you would like syslog to take care of your logs,
change `'stderr'` to `'syslog'`, or even `'syslog,stderr'`. If you go for
syslog, don't forget to configure syslog itself too; for more info, see
link:#link-logging[official documentation].

....
logging_collector = on
....

In case of logging to `stderr`, `postgres` will grab all the logs if you
enable the `logging_collector` option.

This is default option:

....
log_filename = 'postgresql-%a.log'
....

A preferred method could be to name log files by date when they were
created:

....
log_filename = 'postgresql-%G-%m.log
....

Rotation. This really depends on the app itself. In the case of a simple app with little data in the database, all the logs may be kept persistently on disk without rotation.

....
log_truncate_on_rotation = off
log_rotation_age = 31d
....

Increase number of entries in log:

....
client_min_messages = notice      # default notice
log_min_messages = info           # default warning
log_min_error_statement = notice  # default error
....

If you would like to log slow queries, feel free to use this option:

....
log_min_duration_statement = 1000  # in ms
....

The default log entry doesn't contain much info:

....
FATAL:  Ident authentication failed for user "test"
DETAIL:  Connection matched pg_hba.conf line 84: "host    all             all             ::1/128                 ident"
....

Let's improve it to:

....
2013-12-30 17:51:36 CET testx@::1(50867):postgres [11213] FATAL:  password authentication failed for user "testx"
2013-12-30 17:51:36 CET testx@::1(50867):postgres [11213] DETAIL:  Connection matched pg_hba.conf line 84: "host   all             all             ::1/128                 md5 "
....

You just have to alter the option `log_line_prefix`.

....
# %t -- timestamp
# %u -- user
# %r -- client's host
# %d -- database
# %p -- PID
log_line_prefix = '%t %u@%r:%d [%p] '
....

If you are running only a single database with a single user connecting, it makes more sense to simplify the prefix to

....
log_line_prefix = '%t [%p] '
....

[[final-recipe]]
==== Final recipe

....
log_destination = 'stderr'
logging_collector = on
log_filename = 'postgresql-%G-%m.log'
log_truncate_on_rotation = off
log_rotation_age = 31d
client_min_messages = notice
log_min_messages = info
log_min_error_statement = notice
log_line_prefix = '%t %u@%r:%d [%p] '
....

[[reference]]
== Reference

link:PostgreSQL/README.rpm-dist[Full RPM packaging documentation]

https://wiki.postgresql.org/wiki/Tuning_Your_PostgreSQL_Server[Tuning
performance]

https://www.postgresql.org/docs/9.1/runtime-config-logging.html[Logging
configuration]

https://www.postgresql.org/docs/9.1/static/upgrading.html[Upgrading
PostgreSQL]

https://www.postgresql.org/docs/8.3/static/auth-pg-hba-conf.html[pg_hba.conf
file]

See a typo, something missing or out of date, or anything else which can be
improved? Edit this document at https://pagure.io/fedora-docs/quick-docs.
