Message Delivery Modes

PubSub+ event brokers support the following message delivery modes:

For a detailed explanation, see Message Delivery Modes in the Solace Messaging API Developer Guide.

Direct Messaging

Direct Messaging, also known as Reliable Messaging, provides at-most-once message delivery. Direct messages have the following characteristics:

  • They are not retained for a client when that client is not connected to a PubSub+ event broker.
  • They can be discarded when congestion or system failures are encountered.
  • They can be reordered in the event of network topology changes.
  • They are not acknowledged upon delivery.

Direct messages are most appropriate for messaging applications that require very high-rate or very low-latency message transmission. Direct Messaging enables applications to efficiently publish messages to a large number of clients with matching subscriptions.

Guaranteed Messaging

Guaranteed Messaging, also known as Assured Delivery, provides at-least-once message delivery.

Guaranteed messages are maintained in a non-volatile store; therefore, Guaranteed messages are most appropriate for messaging applications that require persistent storage of the messages they send or intend to receive.

Guaranteed messages have the following characteristics:

  • they cannot be discarded or lost once they are acknowledged by the event broker
  • they cannot be reordered in the event of network topology changes
  • when they are delivered to a durable endpoint, they are retained until they are consumed by a client
  • they are acknowledged upon delivery to a client

The quality of service offered by Guaranteed Messaging is analogous to JMS persistent messaging with durable subscriptions.

To support Guaranteed Messaging, a Solace PubSub+ appliance must have an Assured Delivery Blade (ADB) installed and Guaranteed Messaging and message spooling enabled.