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I guess that leaves us back at square one, there are no true async JDBC libraries out there, those that claim they are, are simply wrapping blocking calls with a threadpool.
RxJava implements Backpressure in which case RxJava’s JDBC will probably ease the queries until the client is ready to handle it, but other than that, I might as well roll my own threadpool on top of an existing ORM (combined with a connection pool to keep the latency down) and use futures to notify the caller that its data is ready - the blocking just moves slightly higher up in the chain.