[singron]

The original cron was programmed this way, but it has to examine every job every tick to check if it should run, which doesn't scale well. Instead, you predict when the next run for a job will be and insert that into an indexed schedule. Then each tick it checks the front of the schedule in ascending order of timestamps until the remaining jobs are in the future.

This is also a bad case in terms of queueing theory. Looking at Kingmans equation, the arrival variance is very high (a ton of jobs will run at 00:00 and much fewer at 00:01), and the service time also has pretty high variance. That combo will either require high queue delay variance, low utilization (i.e. over-provosioning), or a sophisticated auto-scaler that aggressively starts and stops instances to anticipate the schedule. Most of the time it's ok to let jobs queue since most use cases don't care if a daily or weekly job is 5 minutes late.