Apache Pulsar vs Google Cloud Pub/Sub

Apache Pulsar is a free, open-source distributed messaging and streaming platform built for cloud use. It supports message consumption with less than 10 ms latency and up to one million unique topics in a cluster. Configurable replication across geographic regions and automatic client failover to healthy clusters support multi-region deployments. Tenants and policies control access to data and actions, and can isolate brokers to limit noisy-neighbor effects. Maintained client libraries are available for Java, Go, Python, C++, Node.js, and C#. Built-in connectors move data to and from systems including Kafka, RabbitMQ, MySQL, PostgreSQL, MongoDB, Cassandra, and Elasticsearch. Pulsar Functions process messages with user-defined logic in Java, Python, or Go. Tiered storage can offload data from BookKeeper to blob storage such as S3 for unlimited retention. It can run in Docker or Kubernetes, with a Helm chart for Kubernetes. Encryption, authentication, and authorization are available but are not enabled by default. The 5.0.0-M2 milestone is for early testing and feedback, not production use.

Google Cloud Pub/Sub is a cloud messaging service for asynchronous communication between services that produce messages and those that process them. It is intended for service-to-service use, including streaming analytics, data integration, middleware, and parallel task queues, rather than direct communication with end users or IoT clients. Communication typically has latency around 100 milliseconds. Synchronous cross-zone replication and per-message receipt tracking provide at-least-once delivery; Dataflow supports exactly-once processing of Pub/Sub streams. There are no shards or partitions, and provisioning scales automatically after quota is set. Message controls include seek and replay, dead letter topics, and attribute-based filtering. Pub/Sub offers fine-grained access controls, end-to-end encryption, and HIPAA compliance. It supports REST and gRPC APIs and client libraries for seven languages; API keys are not supported for authentication. The maximum message size is 10 MB. The free monthly tier is free for the first 10 GB of data per month. Pay-as-you-go is $40 a month beyond 10 GB, with throughput listed at $40 per TB and storage at $0.27 per GiB-month.