I fought PostgreSQL (and eventually won)
We had severeral hours of downtime yesterday because of a “fun” PostgreSQL problem (see Beware of your next glibc upgrade for details). Short version: because there are lots of ways to encode text, and they can change subtly when you upgrade your OS, some of your unique database keys may end up being not so unique. This resulted in quite a few Mastodon tables having duplicate rows, despite having unique indexes. It also meant that PostgreSQL was all like “indexes? lol never heard of ’em” and query performance was pretty awful.