Hi, Ok I have solved my problem. So the critical parameters are the NumberOfBuffers and the MaxDirtyBuffers.
Lowering their values and the reserved memory of virtuoso server reduces as well. I had been trying with 170.000 and 130.000. I have not found the optimal ones for best performance since I do not have time. I think someone must be careful not to enable the swap file (i.e., not enough memory), because afterwards the performance becomes a lot worse!
