User:Ttomecek/draft/postgresql

Installation

pg_hba.conf

md5 ident trust reject

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

max_connections = <number>

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

shared_buffers = <memory unit>

This is the entry point. This is telling PostgreSQL how much memory is dedicated to use 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.

effective_cache_size = <memory unit>

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 common.

work_mem = <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 rump up pretty high. Therefore this is tightly bound to max_connections.

For more information about this topic I advise you to read official documentation about tuning PostgreSQL.

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 official documentation)

logging_collector = on

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

log_filename = 'postgresql-%a.log'

This is default option. 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_lin_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

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] '

Upgrade

If you can't start your instance of PostgreSQL server and can see a message in logs stating

An old version of the database format was found.

You should upgrade your database. With version 9 you can use upgrade tool. First you have to install it:

yum install postgresql-upgrade

Then just execute the 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.

This 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 can also upgrade by dumping your database and loading it again. For more information, see official documentation.

Reference

Tuning performance

Logging configuration

Upgrading PostgreSQL