= PostgreSQL

'''

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'''


[[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 first place, you may consider to install newer
version than is packaged for fedora, see http://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 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[`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[`http://lists.freedesktop.org/mailman/listinfo/systemd-devel`] +
`-- Documentation: `http://www.freedesktop.org/wiki/Software/systemd/catalog/be02cf6855d2428ba40df7e9d022f03d[`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 error message in my example, it is not a fresh
installation, but 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 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 update. This
should be fixed already.

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

[[tips-and-tricks]]
Tips and tricks
~~~~~~~~~~~~~~~

For database management is comfortable to use graphical tools such as
phpPgAdmin or pgadmin3

`$ sudo yum install phpPgAdmin` +
`$ sudo yum install pgadmin3`

Or with dnf in Fedora 22 and later versions:

`$ sudo dnf install phpPgAdmin` +
`$ sudo dnf install pgadmin3`

[[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 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 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
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Soon you run into need of creating a user (and database for the user).
First, you have to switch user to interact with postgres:

`# su - postgres`

and then run postgre's interactive shell:

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

postgres=#
....

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

`postgres=# \password postgres`

Lets get back to user creation:

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

this could be done from system shell too:

`$ createuser lenny` +
`$ createdb --owner=lenny carl`

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

The default settings is 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 postgres'
authentication permissive (bear in mind this will greatly expose your
server, so do it _only_ on trusted network — preferably without not
network at all):

`host    all             all             127.0.0.1/32            trust`

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

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

[[optimisation]]
Optimisation
~~~~~~~~~~~~

Default configuration of postgres is severely undertuned. It can handle
simple application with not so often database access but if you require
higher performance, you should configure your instance better. All the
magic is happening in `/var/lib/pgsql/data/postgresql.conf\``. Also
logging mechanism is configured not very intuitively.

[[performance]]
Performance
^^^^^^^^^^^

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

`max_connections = `

`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 = `

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

`effective_cache_size = `

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 rump up
pretty high. Therefore this is tightly bound to `max_connections`.

`work_mem = `

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

[[logging]]
Logging
^^^^^^^

By default, logs are rotated every week and you don't find much
information in there (one could miss log level, date, time, ...). Also
for simple web applications I prefer to increase verbosity.

`log_destination = 'stderr'`

This is just fine. If you would like syslog to take care of your logs,
change it 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 `logging_collector` option.

This is default option:

`log_filename = 'postgresql-%a.log'`

Much preferred 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 case of simple app
with a few data in 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`

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"`

Lets 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 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 single database with single user connecting, it
would make 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]

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

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

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

http://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.
