Clarification about SNS Fifo max throughput and quotas

Your understanding is mostly correct, but there are some important clarifications to make:

1. SNS FIFO topic throughput: The current quota for Amazon SNS FIFO topics is indeed 3,000 messages per second per topic. This is a significant increase from the previous limit and applies to each individual FIFO topic, not per region.

2. Message group throughput: Within a FIFO topic, each individual message group can deliver a maximum of 300 messages per second. This is correct and helps maintain strict ordering within each message group.

3. Topic vs. Region quota: The quota of 3,000 messages per second is applied per topic, not per region. This means you can have multiple FIFO topics in a region, each capable of handling up to 3,000 messages per second.

4. Maximizing throughput: Your understanding about being able to have 300 messages per second in 10 different message groups, totaling 3,000 messages per second without throttling, is correct. This is an optimal way to utilize the full capacity of a FIFO topic while maintaining message ordering within each group.

5. Throttling: If either the per-topic limit (3,000 messages/second) or the per-message group limit (300 messages/second) is exceeded, AWS will indeed throttle the requests, likely resulting in a 429 (Too Many Requests) error.

It's important to note that to achieve maximum throughput, you should distribute your messages evenly over a large number of message group IDs. This allows SNS to process messages from different groups in parallel while maintaining strict ordering within each group.

Also, keep in mind that when working with high-throughput FIFO topics, it's recommended to enable high throughput mode on any subscribed Amazon SQS FIFO queues to ensure they can handle the increased message flow.
Sources
Amazon SNS increases default FIFO topic throughput by 10x to 3,000 messages per second
Amazon SNS message grouping for FIFO topics - Amazon Simple Notification Service