You wouldn't want to replace RDS (or MySQL/postgres) with Redshift for OLTP workloads. Redshift is built for analytics and complex query workloads. The major benefit is the ability to do MPP (Massive Parallel Processing) and distribute the work out to nodes. I believe you can have up to 100 nodes in the cluster with the 8XL machines and 32 with the single XL.
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You wouldn't want to replace RDS (or MySQL/postgres) with Redshift for OLTP workloads. Redshift is built for analytics and complex query workloads. The major benefit is the ability to do MPP (Massive Parallel Processing) and distribute the work out to nodes. I believe you can have up to 100 nodes in the cluster with the 8XL machines and 32 with the single XL.