What can I do to monitor "out of shared memory" issues?
To monitor postgres logs you can navigate to cd "/usr/local/var/postgres" where you will find the server.log file.

If you want to watch the log in action you can pass the following command into the terminal tail -f server.log

Run your application in the background and if there is an issue occurring in postgres the server.log will catch it.

In my case, I ran RSpec in the background as that's where I saw the original "out of shared memory" message occur. The postgres log picked it up when it happen.