At my last job I made a thing that took in tens of millions of records from Kafka, did some processing, plopped stuff into Postgres, and moved along. It wasn't

At my last job I made a thing that took in tens of millions of records from Kafka, did some processing, plopped stuff into Postgres, and moved along. It wasn't hard, but getting throughput was difficult to achieve my throughput goals with regular blocking JDBC. Eventually I moved to an async-non-blocking model, and for my initial tests it went great, stuff returned almost immediately and I could grab the next one. The problem is that, sort of by definition, non-blocking stuff doesn't really know when it's going to complete right away, so it just kept enqueuing stuff until it ate all my memory. I figured out pretty early on what was happening, but the other people on my team really seemed to struggle with the concept of backpressure, I think because they weren't really used to a non-blocking model. You kind of get backpressure for free with blocking code. Eventually I was able to solve my problem using a BlockingQueue,