Time of the element as seen at source or aligned after a reduce operation.
HTTP-style headers attached to the message.
Set of keys in the (key, value) terminology of map/reduce paradigm. Messages are grouped by these keys within a session.
The message payload as a Buffer. Contains the actual data to be processed in the session.
Watermark timestamp. A guarantee that no messages older than this time will arrive.
Input datum for session reduce operations. Contains message data, keys, timestamps, and headers.