Apache Pulsar vs MQTT: What are the differences?

Introduction

Apache Pulsar and MQTT are both messaging protocols used for communication between applications and devices. While they have some similarities, such as being lightweight and supporting publish-subscribe messaging patterns, there are key differences that set them apart.

1. Scalability: One of the major differences between Apache Pulsar and MQTT is in terms of scalability. Apache Pulsar is designed to be highly scalable, being able to handle large message volumes and support thousands of topics and subscriptions. It achieves this through the use of a multi-layered, hierarchical architecture that allows for efficient data routing and load balancing. MQTT, on the other hand, lacks such a hierarchical design and may face challenges in scaling to handle larger deployments.

2. Persistent Storage: Another important distinction is in the way Apache Pulsar and MQTT handle message persistence. Apache Pulsar provides built-in support for persistent storage of messages, allowing them to be stored on disk and retrieved even in the event of a failure. This makes it more suitable for scenarios where message durability is critical, such as in financial systems or IoT applications. MQTT, on the other hand, does not have native support for persistent storage and relies on external mechanisms to ensure message persistence.

3. Message Acknowledgement: Apache Pulsar and MQTT differ in their approach to message acknowledgement. In Apache Pulsar, messages are acknowledged on a per-consumer basis, meaning that each consumer in a subscription group acknowledges the messages it has consumed. This allows for fine-grained control over message acknowledgement and can help avoid message duplication. In MQTT, acknowledgement happens at the individual message level, where each message needs to be explicitly acknowledged by the consumer. This approach provides more flexibility but may require additional logic to handle message deduplication.

4. Schema and Type Support: Apache Pulsar provides built-in support for schema and type enforcement, allowing for the definition of a schema for the messages being exchanged. This ensures that messages conform to a specific structure and data type, enabling strong data validation and compatibility checks. MQTT, on the other hand, does not have native support for schema and type enforcement, and message validation needs to be implemented externally.

5. Brokers and Topics: Apache Pulsar and MQTT differ in their terminology and concepts of brokers and topics. In Apache Pulsar, brokers are responsible for message storage and distribution, while topics represent the logical channels for message exchange. MQTT, on the other hand, uses the concept of a broker to facilitate communication between publishers and subscribers, with topics representing the specific subjects of interest.

6. Supported Programming Languages: Another notable difference is in the programming languages supported by Apache Pulsar and MQTT. Apache Pulsar provides client libraries for a wide range of languages, including Java, Python, Go, and C++. This allows developers to use their preferred language for building applications on top of Apache Pulsar. MQTT also supports multiple programming languages, with client libraries available for popular languages such as C, Java, and Python.

In summary, Apache Pulsar and MQTT differ in terms of scalability, persistent storage, message acknowledgement, schema support, broker and topic concepts, and supported programming languages.