> Do you really need a queue? (Alternative: periodic polling of a DB)

In my experience it’s not the reads, but the writes that are hard to scale up. Reading is cheap and can be sometimes done off a replica. Writing to a PostgreSQL at high sustained rate requires careful tuning and designs. A stream of UPDATEs can be very painful, INSERTs aren’t cheap, and even a batched COPY blocks can be tricky.