ActiveMQ vs Apache Pulsar: What are the differences?

Introduction In this article, we will explore the key differences between ActiveMQ and Apache Pulsar, two popular messaging systems used in distributed applications.

1. Message Model: ActiveMQ follows the traditional publish-subscribe and point-to-point messaging models, where messages are sent to a topic or a queue respectively. On the other hand, Apache Pulsar introduces the concept of a "topic" which can support both publish-subscribe and event streaming paradigms, allowing for greater flexibility in message distribution.

2. Architecture: ActiveMQ is based on the Java Message Service (JMS) standard and is built using a classic broker-based architecture. It uses a central broker to handle message routing and delivery. In contrast, Apache Pulsar adopts a distributed messaging architecture, using the powerful concept of "bookies" that store and replicate messages across multiple nodes, ensuring high availability and fault tolerance.

3. Scalability and Performance: ActiveMQ has limitations in terms of scalability as it relies on a single broker for message handling. It can suffer from performance bottlenecks when dealing with a large number of messages and high throughput. In contrast, Apache Pulsar has a highly scalable and performant architecture, providing seamless horizontal scalability by allowing independent scaling of compute and storage resources. This makes Pulsar more suitable for handling massive workloads.

4. Multi-Tenancy: ActiveMQ doesn't natively support multi-tenancy, which means it is not efficient for hosting multiple isolated messaging environments within a single deployment. On the other hand, Apache Pulsar has built-in support for multi-tenancy, enabling organizations to create separate namespaces, topics, and access control policies for different departments or teams, enhancing resource isolation and security.

5. Message Durability: ActiveMQ provides message durability through features like persistent messaging and durable subscriptions. However, it relies on traditional storage options like disk-based storage, which can impact performance in certain scenarios. Apache Pulsar, on the other hand, uses a powerful combination of in-memory and durable storage for messages, ensuring high-speed message persistence without sacrificing performance.

6. Compatibility and Ecosystem: ActiveMQ supports the JMS standard and provides extensive support for integration with various Java-based frameworks and applications. It also has support for other protocols like AMQP and MQTT. Apache Pulsar, in addition to supporting the Pulsar-native messaging protocol, provides compatibility with the Apache Kafka API, allowing seamless migration of existing Kafka applications to Pulsar.

In summary, ActiveMQ and Apache Pulsar differ in terms of their message models, architecture, scalability, multi-tenancy support, message durability, and compatibility with other systems. Apache Pulsar offers a more modern and scalable messaging architecture with enhanced features like multi-tenancy and better performance, making it a suitable choice for demanding distributed applications.