Running Jobs when DB is free on Ruby on Rails Heroku

Question

I have a ruby on rails app that uses Heroku. I have the need to run things like import/export tasks on our db that lock up the whole system since they are so heavy on the DB. Is there a way to tell the system to only run these tasks when the database is not being used at that second?

Answer 1

There is no built-in way to schedule a job like this. There are a few things you can do, though.

• Schedule the jobs to run during the least busy hours of the day. That will depend on your business, customer base and so on, but hopefully there is a window that is more suitable than others.

• You could write your batch job to run for a longer time, doing small units of work. Between each unit of work, sleep for a few seconds, or take a look at the current load average and decide what to do based on that. This should lower the impact of the batch jobs.

• Have the website update a "lock" somewhere, either in the database or in a memcached or something. If your normal website usage updates the database, you could look at the existing updated_at. Then only do batch work when there hasn't been any activity for a while. This doesn't guarantee that a new user won't pop in at the same time your batch job runs, of course, but could be a way to find a window where the site is less used.

Answer 2

Have you looked into using Background Jobs / Workers on Heroku? It's also worth reading about Heroku's Delayed Job queuing system