Choosing a Backend

Stem separates delivery from stored state:

Situation	Broker	Store
Tests and demos	In-memory	In-memory
Shared queue	Redis	Redis or Postgres
SQL visibility	Postgres	Postgres
Embedded service	SQLite	SQLite

In-memory state is process-local and not restart-durable. A persistent store does not make effects exactly once; handlers still need idempotency. See Persistence and Broker Overview. Check the package version your application resolves before copying adapter setup: source checkouts and pub releases may expose different APIs.