Session Window

The Session Window buffer groups messages into sessions defined by activity gaps. A new message extends the current session; if no message arrives within the configured gap duration the session is closed and all of its accumulated messages are emitted as a single batch. An optional join configuration lets you run a SQL join across multiple input sources at emission time.

Configuration

Field	Type	Required	Default	Description
type	string	yes	—	session_window
gap	duration	yes	—	Maximum idle time between messages in a session. When the gap elapses with no new messages, the session is flushed. Examples: 1ms, 1s, 1m, 1h.
join	object	no	—	Optional SQL join configuration applied to emitted batches.

join

Field	Type	Required	Default	Description
query	string	yes	—	SQL query joining batch data from different input sources.
value_field	string	no	—	Name of the binary field holding the message payload. Defaults to the engine default binary value field.
codec	object	yes	—	Codec used to decode message batches before joining.
thread_num	integer	no	—	Number of worker threads used for parallel decoding during the join.

The codec field is a CodecConfig object: a type string selecting the codec plus any codec-specific fields.

Examples

Basic Configuration

buffer:
  type: "session_window"
  gap: "5s"

With Join Configuration

buffer:
  type: "session_window"
  gap: "10s"
  join:
    query: "SELECT a.user_id, a.event_type, b.metadata FROM events a JOIN metadata b ON a.user_id = b.user_id"
    codec:
      type: "json"