Say you're running a website which generates a large number of tasks that should be run at particular times (e.g. reminder emails).
You could run a cron which SELECTs a database table for unprocessed events before the current time (or even a long running process that polls the table), but this seems messy. On the other hand, as far as I know most producer/consumer messaging systems don't support arbitrary priorities.
How to approach this?