Reactive Panache MongoDB Always Emits On Event Loop

[ayhanap]

I am using Reactive Panache MongoDB with ReactivePanacheMongoRepository<Entity>. My problem is; Mutiny objects like Unis and Multis returned from MongoDB operations like findById() etc. always emit on Event Loop. I usually map and transforms these reactive objects and all of my other manipulations are also happening on EventLoop.
This is because Unis created at https://github.com/quarkusio/quarkus/blob/main/extensions/mongodb-client/runtime/src/main/java/io/quarkus/mongodb/impl/Wrappers.java specifies emitsOn, which overrides default Mutiny Worker Context.

Is there a way I can change this behavior without manually setting another executor on every reactive object that I get from DB operations?

[quarkus-bot[bot]]

/cc @FroMage (panache), @evanchooly (mongodb), @loicmathieu (mongodb,panache)

[loicmathieu]

This is a design choice of the MongoDB reactive client, nothing specific to MongoDB with Panache.

@cescoffier maybe you can share some light ?

[ayhanap]

Thanks for your answers, @cescoffier after writing the question I already figured this out (Which I knew but..) and I only moved one little long-running file upload operation to another executor.

But then there is one thing @Transactional forces me to use another executor at the start. But other reactive objects created inside defaults to event loop again.

So right now I only have to switch to another thread to start transaction and some long running non reactive works.

[cescoffier]

Yes, that's expected. Isolate the blocking chunks (transactional or not), and run them on a worker thread pool.

[loicmathieu]

@ayhanap, MongoDB transactions are not supported by reactive MongoDB with Panache

[ayhanap]

I see, only the non reactive api supports it I guess. Do you think I can manage transaction manually with QuarkusTransaction.begin(); while still using the reactive api?

[loicmathieu]

MongoDB supports transaction, but we only integrate its support inside the synchronous client not the reactive one (this is possible, we just didn't do it yet). And there is no easy way to do it manually (a ClientSession must be pass to all calls to the client).