Postgres is usually run automatically on my laptop. I also have a weekly cronjob that does
brew update and
brew upgrade which sometimes bumps the version of portgres that I'm running. Newer versions of the postgres server software aren't necessarily compatible with the older version's data directory structure, and so you need to "upgrade" your database to see all of your old data in the upgraded postgres server.
Trying to start the database manually with
pg_ctl -D /usr/local/var/postgres -l /usr/local/var/postgres/server.log start
Which gives an error message and tells me where to look (note that I passed in the log directory when I ran the command)
waiting for server to start.... stopped waiting pg_ctl: could not start server