BlockHound VS r2dbc-postgresql

There is a great tool called Blockhound we can use to detect if/when we have a blocking call in our application. This way, we can ensure that we don't break the non-blocking nature of our application by mistake while developing new features. Setting it up is fairly straightforward.

There's even a test library to detect them: https://github.com/reactor/BlockHound

One of the talks in my current portfolio is Migrating from Imperative to Reactive. The talk is based on a demo migrating from Spring WebMVC to Spring WebFlux in a step-by-step approach. One of the steps involves installing BlockHound: it allows to check whether a blocking call occurs in a thread it shouldn't happen and throws an exception at runtime when it happens.

The first step is to make the application compatible with GraalVM. We need to remove Blockhound from the code. Blockhound allows verifying that no blocking code runs in unwanted places. It's a Java agent that requires a JDK, not a JRE. It's great for a demo, but it has nothing to do with a production application.

Now that we have an application, let's turn it into a reactive application. For this, we will replace Spring Web dependency with Spring WebFlux, Spring Data JPA with Spring Data R2DBC. We will also add R2DBC dependency for our H2 database. R2DBC works with a reactive driver so it will integrate nicely with the rest of our application to allow us database access in a non-blocking way.

However, if you really expect a lot of users (especially concurrent ones) to use your API, you should delve into the world of reactive programming. Use tools like RxJS (JS/TS) or Project Reactor (Java) in such a case, preferably in combination with a broker like Kafka or RabbitMQ. R2DBC is also great for a data store. Then of course if you want to go one step further, there also exists the less popular but very interesting Actor model which Akka easily has ported into Java.