Experts: Who can do this ..... ?
The most prominent characteristics of Add-ons
* Turn on or off
* Do not modify the templates
* Consistency automatic with colors Style Forum
* The emergence of a number Users Online + Number of Visitors Online
* The appearance of the names of Members Online
It has been tested with several thousand records in the session activity list.
The way it works is there is a Cron entry that runs every 1 minute by default but you would probably want to reduce this down on really busy boards.
The Cron entry takes about 10 seconds to run if there's about 5,000 users online.
As I'm sure you can imagine, there has to be a balance between caching and how live and relevant the data is. If It had no caching, effectively every page load for every user would take 10 seconds. So the caching mechanism takes all of this away.
So to answer your question. In terms of page loads - there are NO additional queries and performance should not be affected.