PostgreSQL is a popular ACID-compliant database engine. It has been my go-to database engine for nearly eight years. I have always used PostgreSQL in a Linux environment, but a month ago, I installed PostgreSQL on macOS through Homebrew. This was to avoid needing to boot multiple Vagrant virtual machines.

Since I migrated, I have noticed that Homebrew failed to start the PostgreSQL service many times.

ActiveRecord::ConnectionNotEstablished

connection to server at "localhost" (::1), port 5432 failed: Connection refused 
Is the server running on that host and accepting TCP/IP connections?
connection to server at "localhost" (127.0.0.1), port 5432 failed: Connection refused
Is the server running on that host and accepting TCP/IP connections?

This might be because the service does not shut down properly when the computer shuts down, and a PID file is not being removed. Removing this file is all you need to do.

rm -rf /usr/local/var/postgres/postmaster.pid