I have uploaded about 3700 xml-files (450mb) to db.
 CPU usage at that time was about 100%.
 Is there any way to reduce the server load?
 May be basex has some kind of settings?

Usually the I/O usage should be higher than the CPU usage. How much
RAM do you have, and how many CPUs cores are available on your system
(I guess only 1 of the cores was used)?