Messages
Messages are the basic unit of Macrometa streams. Producers publish messages to streams, and consumers process the message and send and acknowledgment.
A message has the following properties:
| Properties | Description |
|---|---|
| Value | The data carried by the message. All GDN messages carry raw bytes. |
| Key | Messages can optionally be tagged with keys, which can be useful for things like stream compaction. |
| Properties | An optional key-value map of user-defined properties. |
| Producer name | The name of the producer that sent the message. Producers are automatically named, or you can name them. |
| Sequence ID | Each GDN message belongs to an ordered sequence on its stream. A message's sequence ID is its order in that sequence. |
| Publish time | The timestamp when the message was published. Automatically applied by the producer. |
| Event time | An optional timestamp which other applications can use to track events. Default is 0. |
By default, GDN does the following:
- Deletes all messages that have been acknowledged by a consumer.
- Stores all unacknowledged messages in a message backlog for up to three days.
GDN streams has two features, however, that enable you to override this default behavior:
- Message retention enables you to store messages that have been acknowledged by a consumer.
- Message expiration enables you to set a time to live (TTL) for messages that have not yet been acknowledged.
All message retention and expiration is managed at the geofabric level. You can also add a message queue to a specific stream limit the number of messages in the backlog.
The following diagram illustrates both concepts:
note
Contact support@macrometa.com if you need to change the message expiration TTL.