Threads and Room

@Insert, @Update, and @Delete-annotated methods are synchronous, performing their work on the current thread. Hence, they should only be called from a background thread.

@Query methods that return entities, int, tuples, etc. directly also are synchronous. However, @Query methods that return an RxJava type (e.g., Flowable) or a LiveData are not synchronous. Instead, the real work will be performed on a background thread.

As noted earlier, we will explore what this “LiveData” is later in the book. For now, take it on faith that it is another piece of the Android Architecture Components, one that offers an alternative to RxJava for reactive programming.