Suggested initial values for radioactivity and cut-off energy

Your setup would greatly emphasize creation of a thread. One way to think about is that 20 comments equals 1 creation (roughly). I think that there's no shortcut for defining these values but to try to track the site activity and heuristically try to think which threads should be hotter than the others, and try to reverse engineer proper values from there. Once the site is active, you can always fine-tune the energy values afterwards.

About the cut-off energy. Basically, the cut-off energy threshold is performance optimization. Don't set it so high that nodes that get some meaningful activity don't get the energy value reset to zero at the next cut-off. What I mean is that if the node has 0 energy initially and gets 5 views (=1 unit) per minute, and cut-off (10 units) is performed every minute, the node will never have more than 5 units of energy because of the cut-off.

Having hundreds of nodes, or maybe even tens of thousands of nodes in the radioactivity table is probably no big deal for most sites, as usually the operations are really straightforward, like get top 10 nodes of some type ordered by energy etc. So keeping it reasonably small is probably safe. The idea is to remove the entries that absolutely no-one is interested in, as they're not meaningful. Think like: "If the energy is below the threshold, it's effectively 0." Try setting the threshold initially low (like half a view) and only raise it if you have performance problems.

Maybe some of these thoughts should be included in the documentation. Anyways, hope this helps.

Issue triage: Closing issue, the 6.x branch is no longer maintained.

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I agree, this is useful. Also the relation between Granularity and cron should be explained:

Granularity is the time between energy calculations. For development, where cron is executed manually, it is useful to set the Granularity low. But for a production environment, the granularity should be set to a value equal or higher than cron. If you want your popularity per day, set the Granularity to 86400 seconds (=24 hours). Cron will now re-calculate the popularity once per day.

The readme and on-line documentation (https://www.drupal.org/docs/contributed-modules/radioactivity) have now more detailed description of the various profiles and their configuration options.

Closing the issue now. If you need support and want more information, feel free to open a new support issue.