ECU

AWS Cassandra: Cassandra, NUMA and EC2

AWS Cassandra and NUMA

The i3.8xlarge, c4.8xlarge, m4.10xlarge, and above EC2 instance types use more than 1 CPU, which means NUMA controls are available.

A good read on this is from Al Tolbert’s blog post.

The quickest way to tell if a machine is NUMA is to run “numactl –hardware”. -Al Tobey blog post on Cassandra tuning

NUMA stands for Non-Uniform Memory Architecture. Modern x86 CPUs contain an integrated memory controller. Multi-socket system, have two memory controllers. Each CPU gets a share of the memory. If one CPU socket needs memory that another CPU socket has, the memory is transferred. Transferring this memory between CPUs is more expensive than if the memory only existed in one CPUs memory. When a JVM thread only uses memory local to one CPU, things go fast, and if not slower (10 CPU cycles vs. 100 or some order of magnitude).

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Cassandra AWS CPU Guidelines

Cassandra CPU requirements in AWS Cloud

Cassandra is highly concurrent. Cassandra nodes can uses as many CPU cores as available if configured correctly.

What are vCPUs and ECUs?

An Amazon EC2 vCPU is a hyper thread, often referred to as a virtual core. Think of it as a physical thread of execution. It is able to run one thread at a time (which of course could be swapped out).

An Amazon ECU is some made up term that AWS used to use which was the power of the Intel Pentium chip that they used on the earliest incarnations of EC2. 50 ECU would be like 50 Pentium chips from a bygone era. Ignore ECUs.

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