link: Message brokers

Quality of Service

Diagram

Overview

Delivery semantics define how messages are delivered and processed in a messaging system. They are crucial in ensuring that messages are handled correctly according to the application’s needs. There are three primary delivery semantics:

At Most Once

Info

• Definition: A message is delivered not more than once. Messages may be lost, but they are not redelivered.
• Use Cases: Suitable for scenarios where a small amount of data loss is acceptable, such as monitoring metrics or non-critical log data.
• Example: Sending periodic updates where missing one update is not critical, like temperature readings from a sensor.

At Least Once

Info

• Definition: Each message is delivered at least once, but it may be delivered multiple times. No message should be lost.
• Use Cases: Ideal for use cases where message loss is unacceptable, but duplicates can be tolerated or handled, such as logging systems or metrics collection.
• Example: Sending notifications where ensuring the message is received is crucial, even if it means the recipient might get the same notification more than once.

Exactly Once

Info

• Definition: Each message is delivered exactly once, ensuring no duplicates and no message loss. This is the most stringent delivery semantic.
• Use Cases: Critical for financial transactions, payment processing, trading, or any system where duplication or loss of messages cannot be tolerated.
• Example: Processing orders in an e-commerce system where duplicating an order or losing an order can have significant financial implications.