The Session Store keeps the state that makes MQTT sessions persistent: which clients are connected, what they are subscribed to, and which QoS 1/2 messages are still in flight. It is the reason a device can drop off the network and resume exactly where it left off.
Storage profile
Redis, in-memory with disk persistence for crash recovery. Entries are keyed
by client_id and carry a TTL so abandoned sessions expire automatically
instead of leaking memory across the fleet.
The schema captures the session, its subscriptions, any buffered in-flight messages, retained messages per topic, and the last-will message. The ERD is embedded on the Overview tab.
clean_start = false) survive disconnects until
expires_at; clean sessions are discarded the moment the client drops.INFLIGHT_MESSAGE tracks the QoS handshake state so redelivery resumes
correctly after a reconnect.WILL_MESSAGE is published automatically by the
Topic Router
if a client disconnects ungracefully — the platform’s crash signal for a
device.