Apache Pulsar vs Mosquitto: What are the differences?

# Apache Pulsar vs. Mosquitto

Apache Pulsar and Mosquitto are both popular messaging systems, but they have key differences that set them apart. Here are the top 6 differences between Apache Pulsar and Mosquitto:

1. **Scalability**: Apache Pulsar is designed for massive scalability, able to handle millions of topics and subscriptions with ease. Mosquitto, on the other hand, is more suited for small to medium scale deployments, limited by its architecture in handling large volumes of messages.

2. **Multi Protocol Support**: Apache Pulsar supports multiple messaging protocols like MQTT, Apache Kafka, and WebSockets, providing flexibility for different use cases. Mosquitto, however, primarily focuses on supporting the MQTT protocol, restricting its compatibility with other protocols.

3. **Data Retention**: Apache Pulsar offers more advanced data retention policies, allowing users to define rules for message expiration, retention limits, and compaction. Mosquitto has basic data retention capabilities but lacks the advanced features that Apache Pulsar provides.

4. **Multi-tenancy**: Apache Pulsar natively supports multi-tenancy, enabling different teams or organizations to share the same cluster while maintaining isolation and resource guarantees. Mosquitto lacks built-in support for multi-tenancy, leading to potential conflicts when multiple users or groups access the system concurrently.

5. **Reliability and Fault Tolerance**: Apache Pulsar provides built-in features for automatic data replication, failure recovery, and geo-replication, ensuring high availability and fault tolerance. Mosquitto has limited support for replication and fault tolerance, making it more prone to issues in case of hardware failures or network disruptions.

6. **Extensibility and Customizability**: Apache Pulsar offers a more extensible architecture with support for plugins, custom connectors, and streamlined integration with external systems. Mosquitto, while being lightweight and easy to deploy, lacks the extensive customization options that Apache Pulsar provides.

In Summary, Apache Pulsar and Mosquitto differ in scalability, protocol support, data retention, multi-tenancy, fault tolerance, and extensibility, catering to different messaging system requirements.