THEMIS collects datas from various hardware services. Once collected from a sensor, data is processed by THEMIS/emoncms through a MQTT broker called mosquitto and a key value in memory database called Redis. At the end of this processing cycle, data is stored in binary feeds on a flash memory.
When receiving new datas from sensors, hardware services (ota2, modbus, emonhub) publish one or several json payload(s) on one or several topic(s) of the MQTT broker.
For a node identified by its id nodeid, the topic is emon/nodeid or emon/userid/nodeid in multi-user mode.
For a temperature and humidity sensor, the payload can be {temp:24.7, rh:56.8}
When a json payload is received from the broker, the emoncms_mqtt service updates a hash called lastvalue and a sorted set called buffer in redis.
At a regular time step (300s by default), the feedwriter service reads the redis buffer and updates the binary feeds.
As already mentionned, please note that injecting last values monitored into the redis database is part of the whole cycle processing.