I have one standard web dyno and worker dyno connected to the same standard 0 database.
The worker dyno runs background jobs that insert a lot of data into the database. I feel like I have noticed slower response times while browsing my site when the workers are running.
I'm always well below the 120 connection limit. Am I imagining this or does it have an impact on read time? If so, how do people mitigate it?
From the database's perspective, there is no difference between connections originating from the web dynos and worker dynos; they're both just clients of the database.
If your worker dynos are doing heavy inserts all the time, then they could certainly impact query performance as this places a lot of load on the database; how this impacts your web response times is specific to your particular application.
I would recommend starting by looking at Heroku Postgres tools for database performance tuning. https://devcenter.heroku.com/articles/heroku-postgres-database-tuning
Without knowing more about your application I would say you could start with looking at the slowest queries related to your web requests and compare them to query time with and without the workers enabled.
