[SOLVED] New Lemmy Admin

EDIT: With thanks to u/code@lemmy.mayes.io, I have a solution for cleaning up the one table that is growing ridiculously in size and that is the activity table. A TRUNCATE activity; command cleaned that right up. A word of caution is in order because the Lemmy instance must be shutdown completely and only the postgres container running if you're using docker.

As a new Lemmy admin, I think I really need to learn PostgreSQL administration because I need a way to keep my database from ballooning in size and there are no management tools built yet for it. Would someone be so kind as to recommend a good website for learning PostgreSQL? This would also help me maintain my mastodon instance.