We currently impose a soft limit on the amount of CPU resources each user is allowed to consume in their consoles. Paying users get more than free users.
The general idea is that everyone should be able to do a fair bit of number-crunching, but anyone that sits there consuming 100% CPU for a long time will eventually end up in the tarpit.
Tarpit counters are currently reset once a day. You can check your own limit and how much you've used today on the Consoles page
What it means is that your processes get lower priority than everybody else's, but they do still run. Once processes are in the tarpit however, we reserve the right to kill them if your usage starts to negatively impact other users too much -- and in particular, if you somehow manage to use more than ten times your quota.
Being in the tarpit does not affect your web apps.
Currently the tarpit only applies to console, scheduled tasks and always-on tasks. Always-on tasks are stopped and restarted when you go into and out of the tarpit. There is a short period during this when the task is not running.
Here comes the upsell! Naturally, paying users get higher limits than free users, so if you're finding yourself in the tarpit a lot, you might want to think about upgrading your account.
The seconds are seconds of CPU time - so any time that the processor spends working on your code. Internally, we measure it in nanoseconds.
If you kick off a process with a busy loop, you should find yourself using up your allowance at approximately 1 second per second. It's a cumulative counter though, so if you kick off multiple processes at the same time, you can get through it faster!
We display the usage on the main consoles page,