Reactive I/O layer transition in Quarkus 3.0 affecting Hibernate Panache

Answer

In Quarkus 3.0 the reactive I/O layer has not been replaced by Netty; Vert.x remains the core reactive engine and Netty is used only as the underlying transport. Consequently, reactive transaction management in Hibernate Reactive Panache continues to run on the Vert.x event loop, and there is no inherent performance or threading penalty from the Vert.x‑to‑Netty view.

Confirmed facts

• Quarkus 3.0 still depends on Vert.x as the reactive core; the quarkus-vertx extension provides the API surface but does not duplicate event loops.
• Hibernate Reactive Panache relies on Mutiny, which binds database operations to the Vert.x event‑loop thread.
• Netty is employed internally by Vert.x for socket I/O; swapping the transport does not change the threading model.

Likely explanation (based on model knowledge)

Because the event loop is unchanged, the overhead of reactive transactions stays the same: each database call is processed on a Vert.x‑event‑loop thread, yielding non‑blocking behavior with minimal context‑switch cost. Adding the quarkus-vertx extension only brings in the Vert.x API classes; it does not create a second event loop or increase native image size significantly.

Steps to bridge Vert.x‑dependent logic without pulling the full stack

1. Add the quarkus-vertx extension if you need to inject or program against Vert.x types:

   ./mvnw quarkus:add-extension -Dextensions="quarkus-vertx"

2. Inject Vertx where required:

   @Inject io.vertx.core.Vertx vertx;

3. Use the injected Vertx instance to obtain the current event loop or create futures; avoid blocking calls on this thread.
4. Verify that the application still runs on Vert.x threads by checking log output for thread names like vert.x-event-loop-thread-*.
5. Test in native mode to ensure no ClassNotFoundException appears:

   ./mvnw package -Pnative

If you continue to see ClassNotFoundException for a specific Vert.x class, please indicate the exact class name so we can confirm whether the quarkus-vertx extension resolves it or if another dependency is missing.