I would also add that AWS' I/O capabilities are quite poor and expensive. I assume that you have tried purchasing additional IOOPs on that setup to see whether you got an expected speed up? If not you should try that as a diagnostic tool even if you wouldn't want to pay that on an ongoing basis.
I haven't tried increasing available IOPS, but looking at the metrics, I'm far away of the limit, so it doesn't seem to be related, but I will explore this option further.
We have a client that is I/O write bound and it has taken us significant efforts to get it to perform well on AWS. We definitely run our own instances rather than depend on RDS and have always been able to outperform RDS instances which seem to really be focused to provide a PAAS capability for developers who really don't want to have to understand how a db works. Running our identical environment on bare metal is like night & day under any circumstances when compared to AWS.
Client's requirement is AWS so we keep working on it and we like AWS for many things but understand it will always underperform on I/O.
Post actual measurements with and without IOOPs or create your own PG server instance and then people might be able to give you additional insights.
I'll consider your suggestions and I'll back with more info in case I create my own environment, I just wanted to know if the number of schemas/tables could be the cause of high writes levels, in order to discard this hypothesis.
