Message Structure

All messages have a consistent structure.

Message
Header sequencing / metadata / routing
Payload user-defined data

Header

The header is comprised of the following fields:

Field	Responsibility	Description
sequenceNumber	Platform	The unique sequence number assigned by the Sequencer. This provides the platform ordering for the message.
sequencerNanoTime	Platform	The timestamp that the message was received by the Sequencer.
relayNanoTime	Platform	The timestamp that the message was received by the Relay supplying the message to an application.
messageType	Platform	Indicates how the message was delivered to the application: LIVE - the message was received from live platform data. CACHED - the message was supplied from the platform cache.
applicationId	API	The unique identifier of the application that published the message.
applicationSequenceNumber	API	An application-provided sequence number for the publication, useful for publisher-side ordering, diagnostics and reconciliation.
publicationNanoTime	API	An application-provided timestamp associated with publishing the data.
voided	Application	Indicates whether the message should be treated as no longer valid. Voided messages are routed separately and evicted from the cache.
editable	Application	Indicates whether edit requests can be made for this data. Messages are not editable by default.
cacheMode	Application	Controls how the message participates in platform caching. Values are CACHE, CACHE_FOREVER and DO_NOT_CACHE, see Message Caching for details.
payloadSchemaId	Application	Identifies the schema or model namespace of the payload. It tells subscribers which schema family the payload belongs to, but not the specific message type inside that schema. This field is automatically set by the API when using SBE, DTO, Flexible and Custom serialization.
payloadTemplateId	Application	Identifies the concrete type within a schema. This field is automatically set by the API when using SBE, DTO, Flexible and Custom serialization. Subscribers use the (payloadSchemaId, payloadTemplateId) tuple to select the correct decoder.
topicSource	Application	The Topic Source. See Topic Structure.
topicGroup	Application	The Topic Group. See Topic Structure.
topicId	Application	The Topic Id. See Topic Structure.
causeSequenceNumber	Application	Optional sequence number of the incoming message that caused this message to be published. This is useful for cause-and-effect tracking.

payloadSchemaId and payloadTemplateId are used together to identify the payload type. This is the Type component described in Topic Structure and allows subscribers and tooling to select the correct schema, decoder or payload handler.