Apache Pulsar vs Apache RocketMQ: What are the differences?

Introduction

Apache Pulsar and Apache RocketMQ are both open-source messaging systems used for building real-time streaming applications. While they share some similarities, there are key differences between the two.

1. Messaging Model: Apache Pulsar follows a publish-subscribe messaging model, where publishers and subscribers communicate through topics. It supports both one-to-many and many-to-many communication patterns. In contrast, Apache RocketMQ follows a distributed messaging model, with producers sending messages to specific queues or topics, and consumers pulling messages from these queues or topics.

2. Scale and Scalability: Apache Pulsar is designed to be inherently scalable, allowing seamless horizontal scalability across multiple clusters. It provides built-in support for multi-tenancy and efficient data replication. On the other hand, Apache RocketMQ is also scalable, but it focuses more on vertical scalability within a single cluster by supporting partitioning and sharding of topics.

3. Persistence and Durability: Apache Pulsar offers persistent message storage by default, ensuring durability even in the presence of failures. It utilizes a tiered storage architecture with a combination of off-heap, on-heap, and disk storage. Apache RocketMQ, on the other hand, supports both persistent and non-persistent messaging, but it primarily focuses on providing high throughput rather than strong durability guarantees.

4. Message Ordering: Apache Pulsar guarantees strict message ordering within a partition, enabling reliable FIFO processing. It ensures that messages published to a topic are consumed in the same order they were published. In contrast, Apache RocketMQ provides a more relaxed ordering guarantee, allowing out-of-order message consumption within a topic.

5. Cross Datacenter Replication: Apache Pulsar has native support for replicating data across multiple datacenters, providing seamless disaster recovery and geo-distribution capabilities. It ensures strong consistency between datacenters. Conversely, Apache RocketMQ relies on third-party solutions or custom implementations for cross-datacenter replication.

6. Ecosystem and Community: Apache Pulsar has a growing ecosystem with a diverse set of connectors, integrations, and tools. It is backed by a vibrant and active community, which contributes to its rapid development. Apache RocketMQ also has a strong ecosystem and community support, but it may have a relatively smaller community compared to Apache Pulsar.

In summary, Apache Pulsar and Apache RocketMQ differ in their messaging models, scalability approaches, durability guarantees, message ordering, cross-datacenter replication support, and ecosystem/community size.