How to access a blocking data source (e.g., database) in a reactive pipeline?

In a reactive pipeline (for example, using Project Reactor or RxJava), blocking data sources such as databases should be wrapped in non-blocking calls to avoid blocking the reactive execution thread.

Typically, this is done using:

• A Scheduler with a dedicated thread pool for blocking operations (for example, Schedulers.boundedElastic() in Reactor).
• The call to the blocking method is executed within subscribeOn or publishOn with such a Scheduler.

Example in Reactor:

Mono.fromCallable(() -> blockingDatabaseCall())
    .subscribeOn(Schedulers.boundedElastic())
    .map(result -> process(result))
    .subscribe();

Thus, the blocking call is executed in a separate thread, not blocking the main reactive thread, and the result is asynchronously passed further down the pipeline.