DynamoDB DAX metrics

Question

I want to build serverless app using lambda и dynamodb. To create a cluster I must know how particular configuration will work with the structure and the size of my table. To find out it I was going to use CloudWatch metrics, but as it turns out they do not reflect the objective reality and can't show the "needs" of the cluster at a particular moment in time. There may be someone who has encountered such a problem and can suggest how best to determine the cluster configuration with respect to the table parameters, the number and type of requests?

Answer 1

So much of it depends on a particular workload, your expected hit rate, distribution of key accesses, etc. There a few rules of thumb, but these may change over time due to changes in the service, so it's always best to do your own testing with your own workloads:

• Within a family (t2, r3, r4) latency is pretty much constant, although bigger node types tend to be more consistent (lower p99).
• Throughput scales ~linearly with node size (i.e. a 2xl is ~2x the throughput of an xl)
• Throughput scales ~linearly with cluster size
• TPS scales ~linearly with response sizes - if a node handles 50 000 1kB gets, it'll do about 5 000 10kB gets.

My recommendation is figure out your workload, test on a few different cluster sizes to get some baselines, and use the notes above to scale. Do note that DAX doesn't currently allow changing the node type for a cluster, and scaling a cluster out only increases throughput, not cacheable memory.

As for better CloudWatch metrics, it would be helpful to know what you're looking for - it might better to start a thread in the AWS forums for that discussion.