PostgreSQL High Availability Cookbook - Second Edition

How to do it...

We can collect some of the information we want from the database if we have one already. If we already have a PostgreSQL database available, we can execute a query to start our calculations. This works best if used at the most active time of day.

Execute this query as a superuser to get the count of simultaneous active users if you have PostgreSQL 9.2 or higher:

SELECT count(1) FROM pg_stat_activity 
 WHERE state = 'active'; 

Use this query if you have an older version:

SELECT count(1) FROM pg_stat_activity 
 WHERE current_query NOT LIKE '<IDLE>%'; 

If we don't have a PostgreSQL server, we need to make an educated guess. Use these steps to approximate:

1. Work with the application developers to obtain a count of expected clients ...