Event volume (events)

Topic: events

Traded volume per event: one number covering every market on it, so a client showing “$12,430 vol” on an event card need not fetch that event’s markets and add them up.

One topic covers every event, narrowed by the join payload. Ten events is one join, not ten.

Joining

["1","1","events","phx_join",{"event_ids":["<uuid>","<uuid>"]}]

At least one valid event_id is required. As on orderbook, an absent or unusable list is an error, not “no filter”; every event on the exchange is not served here.

{"status":"error","response":{"reason":"event_ids_required"}}

The reply echoes the filter and carries each event’s current value, so a client paints before the next trade:

{"status":"ok","response":{
  "selected_event_ids":["<uuid>"],
  "events":[{"event_id":"<uuid>","volume":"12430.0000"}]}}

An event with nothing recorded is omitted from events, not reported as zero, so “not known yet” stays distinct from “nothing traded”. Its id is still echoed in selected_event_ids.

orderbook and ticker send no snapshot because their producers republish on a cadence. Event volume moves only on a trade, so without this a client sits blank while the event is quiet.

Server pushes

event, one message per event whose value changed:

{"event_id":"...","volume":"12455.0000"}

volume is the event’s lifetime traded volume in dollars across every active market on it, a dollar string; see Wire format.

Every push is the whole current value, not a delta. Replace what you hold for that event_id; never add to it.

Pushes are coalesced to at most one per event per second, and an unchanged figure pushes nothing.

Ignore keys you do not know

Fields will be added: market counts, open interest, event status. Treat an unknown key as ignorable rather than an error and a client written today keeps working.

Changing which events stream

["1","2","events","select_event_ids",{"event_ids":["<uuid>"]}]

Same non-empty rule; an unusable list keeps the current selection and replies with an error. The reply has the join reply’s shape, current values included.

Use Cases

Use case	Message to send
Join for two events	["3","3","events","phx_join",{"event_ids":["<uuid>","<uuid>"]}]
Change which events stream	["3","4","events","select_event_ids",{"event_ids":["<uuid>"]}]
Keep the channel alive	["3","5","events","ping",{}]