Isn’t sidekiq working off Redis? You might be adjusting the Redis concurrency instead. And if I remember correctly even with sidekiq you’re still using normal Rails and ActiveRecord, so a process that’s running 25 sidekiq jobs simultaneously is going to need 25 active record DB conns from the database.yml. I doubt the sidekiq config is overriding it in some way.

But basically if your sidekiq workers and app servers are using the same database.yml values, you’ll need to set the greater of the two on both. I assumed you have different settings on app servers and workers.