How do I set and get custom database variables?

Question

Using PGAdmin III I can right-click on a database, navigate to the Variables tab, and put a variable name-value property on the database itself. Is there a way to customize these? I saw an application_name variable, but I'd like to have an application_version variable.

Answer 1

To add to @dezso's answer, these variables can be changed with

SELECT set_config('class.name', 'value', valid_for_transaction_only::boolean)

and read with

SELECT current_setting('class.name')

See this link for more info: http://www.postgresql.org/docs/9.3/static/functions-admin.html

Answer 2

You have to add the variable to the end of your postgresql.conf like

#------------------------------------------------------------------------------
# CUSTOMIZED OPTIONS
#------------------------------------------------------------------------------
custom_variable_classes = 'general' # list of custom variable class names
general.application_version = 'v1.0'

When restarted, you can add general.application_version manually in PgAdmin (it will not show up in the drop-down - at least not for me). Otherwise, you can use it just like any other PostgreSQL variable.

Update for version 9.2 and newer

From PostgreSQL 9.2 onwards, we don't have to set custom_variable_classes anymore. One can set whatever variable they want - the only limitation seems to be it still has to have two parts:

SET something TO 'bla';
ERROR: unrecognized configuration parameter "something"
SET thing.something TO 'bla';
SET

I guess this is so to avoid collision with the builtin parameters.

• Jeremy Holovacs: Hmmm. No way to do that from a SQL query in the database?
• András Váczi: You have to first define the variables in postgresql.conf. AFAIK this requires restarting PostgreSQL, so you can't do that from SQL.