Hi Dimitrios,
Yes, as mentioned in this thread: Select recordings by trial group, for the time being you need to run a Select Files process first to populate the sFiles variable before using the Search query process. This is on my To-Do list...
However, this should not be related to the issue you reported in this thread, unless I am misunderstanding something. When running the process, it does not update the database tree so there should not be slowdowns. It should be very fast this way actually. The slowdown should be coming from when you use the Search dialog from the GUI, and this is what I was asking you to profile.
Martin