Your schema should store:
- last run time epoch milliseconds
- frequency to run at, in seconds
- other stuff like ids, foreign references, job names, etc.
On startup, partition all your jobs by frequency (60 might mean something run every 60s; 3600 would be hourly; etc)
and then sort by last run time, oldest to newest. Map each set to figure out each job's next run time.
Look at the 0th item in each set to see which has the next run time. Sleep between now and then.
When you wake up, execute your top job. Update its last run time. Add it back to the queue of jobs. Re-partition/sort/map the entire queue; calculate your next run time; rinse and repeat.
There's plenty of opportunity here to improve this, by adding state tracking; offloading the sorting/mapping to your database; periodically refreshing the list of available jobs; etc. but for a naive implementation, this works.
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