Most teams don't need five databases. PostgreSQL's extension ecosystem covers caching, queues, full-text search, and vector search — but the real decision isn't 'can it do it' but 'where does ops cost cross performance needs.'
BullMQ is the most mature job queue in the Node.js ecosystem, backed by Redis, with support for priorities, retries, scheduling, and delayed jobs. DaoDao uses it to handle notification delivery and practice auto-completion scheduling.
Redis is an in-memory key-value store that's blazingly fast. DaoDao uses it to handle three responsibilities at once — API caching, session storage, and BullMQ job queues — all from a single Redis instance.