Since the DB version, table, indexes, and execution plans are the same, you need to compare the configurations of machines and clusters. Comparison highlights Accessibility of processor power, cores used in a single transaction, read speed, memory size and read speed / frequency. I see that Amazon provides a lot of configurations, so perhaps your private cluster is much more powerful than the Amazon RDS instance configuration.
To add above, you can balance the load between CPU, IO and Memory to increase throughput.
source share