@Mixins(value={SQLEntityFinder.class,SQLStateChangeListener.class})
public interface SQLIndexingEngineService
extends StateChangeListener, EntityFinder, ServiceComposite

This is actual service responsible of managing indexing and queries and creating database structure.

The reason why all these components are in one single service is that they all require some data about the database structure. Rather than exposing all of that data publicly to be available via another service, it is stored in a state-style private mixin. Thus all the database-related data is available only to this service, and no one else.