will it harmful for server to run a cron job in every second

Question

For the checking of online users who doesn't log out properly but close the browser, I want to run a cron job in every 2/3 second. (I am updating database in every 10 second when logged in)

Will it harmful for server?

Answer 1

Cron lowest possible frequency is 1 minute so you cannot fire anything more often with it. As for overkill - it may or may not be there, but you need to review the code and load it produces yourself.

Answer 2

You can't run cron jobs more frequently than once a minute so this isn't possible from a cron anyways. You'd have to have a process running in a loop with sleep to achieve this, but the idea is overkill anyways - once a minute is fine.