Absolutely, I think it's all baked into Postgres. Didn't know about publish/subscribe. I was thinking we could use the Postgres LISTEN/NOTIFY and that upon notification the standalone db can query the full HAF server for exactly the data it wants. My understanding of publish/subscribe is very limited, but does it allow to selectively copy over only some of the data from a table, e.g. only custom_json ops with a certain ID? It didn't seem it allows for that from the docs I looked at. And also, I suspect in many instances an API might want not replication but to select and then create its own derivative data, as with the example of the polls protocol where the custom_jsons will be evaluated based on the protocol rules.

But in any case, I fully expect the mechanics of how it is done to undergo iterations as we hopefully build some useful real-world applications and we apply lessons learned. Much more of interest to me is any feedback on the proposed overall approach of creating an API layer made up of a large number of small databases, which get their data from the much smaller number of full HAF servers. Do you have any thoughts on that as an approach?