this is not a bug and by design. Adding any qualifier will make it a bean with the default scope (prototype)

ok, just related to this I wonder - why was prototype chosen as a default scope instead of singleton as it is in Spring? falling back to prototype when any scope is selected has significant impact on the application performance. @wololock discovered this behavior when he was debugging huge memory leak (thousands of repository instances in the memory).

Just to give you more context, there's one nasty corner case when injecting a class with only @Named annotation when it also injects the Micronaut Data repository - such a repository will be instantiated for each prototype. When looking at what is injected in such a case, we will see SomeRepository$Intercepted instead of $SomeRepository$Intercepted$Definition. And since each repository has always alive reference from interceptors from DataInterceptorResolver, those one-time-use repositories stay in the memory forever, GC cannot clean them up.

This was our use case - one of our microservices that was using a few @Named service classes without @Singleton annotation started having huge memory issues. Mem consumption was growing at a pretty fast pace, and when we looked at the heap dump, we saw millions of entries inside DataInterceptorResolver.interceptors and hundreds of thousands of duplicated repositories in memory. Basically, each request that used this unlucky @Named service ended up adding a new repository instance to the memory. I don't know if this behavior applies only to repositories - I see in the debugger of our codebase that other injected beans (like ObjectMapper) are not duplicated, but every repository injected generates a new instance each time the @Named only bean is injected (or requested from BeanLocator).

I guess if non-duplicated Microaut Data repositories were injected in such a case (like it happens with other beans), the default behavior wouldn't produce any weird side-effects.

@wololock Can you please create a spearate issue with a test?

@dstepanov I think I have enough info to add it to my test repo. let me check.

Nevermind, found the problem

Thank you, @dstepanov !

you're fast. here's the test anyway musketyr/named-annotation-bean-issue#1

so this look like a separate bug.

As for Micronaut default vs Spring default one could inverse the question. In CDI and other dependency injectors singleton is not the default.

thanks for explanation @graemerocher. I will keep this in mind. I got the question from my colleague as almost everyone comes from Spring background.