remaining connection slots are reserved - Primary Postgres database process (postmaster) eating all CPU - Installation - Discourse Meta b888 slot

I’ve got a 2-container install on a DO 8GB droplet that is behaving very strangely. There is a postmaster (EDIT: now there are two of them) processing eating 100% CPU. Sidekiq is running, but the Dashboard complains that it’s not checking for updates. There are some logs like PG::ConnectionBad (FATAL: remaining connection slots are reserved for non-replication superuser connections ) /var/www/discourse/vendor/bundle/ruby/2.4.0/gems/pg-0.21.0/lib/pg.rb:56:in `initialize' and Job exception...

Wondering how to resolve PostgreSQL “Remaining connection slots are reserved” error ... As a part of our Server Management Service, we help our customers to fix PostgreSQL related errors regularly.

Which of these is better? 'In' or 'on'? "Schedule the meeting in the remaining slots." "Schedule the meeting on the remaining slots." I want to express that only a certain number of slots are left, and I wish to schedule a meeting ___ one of those.