To help determine which replication instance class might work best for you, let's look at the change data capture (CDC) process that AWS mainframe modernization service's data replication feature with Precisely uses.
Let us assume that you are running a CDC task (ongoing replication). In this case, the replication job has its own publisher and engine, which stores metadata and other information. The reading of transaction logs on the source is kicked off as soon as the replication job on the AWS EC2 instance is started and starts a transactional apply process on the target instance.
- It tracks all transactions and makes sure that it forwards only relevant transactions to the outgoing buffer.
- It makes sure that transactions are forwarded in the same commit order as on the source.
As you can see, there are three important memory buffers in this architecture for CDC. If any of these buffers experience memory pressure, the overall replication can have performance issues that can potentially cause failures.
When you plug heavy workloads with a high number of transactions per second (TPS) into this architecture, you can find the extra memory provided by R5 and R6i instances useful. You can use R5 and R6i instances to hold a large number of transactions in memory and prevent memory-pressure issues during ongoing replications.