Same-Region Read Replicas to Serverless Postgres

Any choice in datastore performance is made up front by choosing how spread out the data is: basically, maximum throughout is the sum of maximum throughput for each storage rack hosting the data. To simplify, if we had a datastore replicating data to 10 instances with peak IOPS of 100k each, we are looking at max 1M IOPS: the fact that we can cheaply scale our CPU instances for Postgres infinitely won't change the upper bound for IO (without scaling the storage too, which is recognized as the slow but avoided part with their implementation).

Network can play a similar role.

And finally, Postgres instances benefit from being long-lived as opposed to serverless (in a more traditional sense): with enough RAM, all the important indexes can stay permanently in the cache thus improving performance by orders of magnitude compared to cold Postgres instances needing to read indexes off disk.

In theory, one could pre-warm memory caches for Postgres read replicas (akin to suspend/hibernate), but depending on the memory size needing to be read from slow storage, it might not really beat simply reloading the indexes.

Obviously, my concerns are related to large databases, but those are the ones usually needing scale out.