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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:

ValueThe data carried by the message. All GDN messages carry raw bytes.
KeyMessages can optionally be tagged with keys, which can be useful for things like stream compaction.
PropertiesAn optional key-value map of user-defined properties.
Producer nameThe name of the producer that sent the message. Producers are automatically named, or you can name them.
Sequence IDEach GDN message belongs to an ordered sequence on its stream. A message's sequence ID is its order in that sequence.
Publish timeThe timestamp when the message was published. Automatically applied by the producer.
Event timeAn 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:



Contact if you need to change the message expiration TTL.