Customer concerned that saveing is too slow, so I started wondering what's wrong with it and marked Log4net NHibernate.SQL DEBUG mode.

And I found that In every save NHibernate generates sql update for every collection loaded in session?
What, why?
Probably there is something wrong in my configuration.

I'm using the ActiveRecord for mapping classes and application is winforms

Please advise?

What do you mean with save ? When you use hibernates Save(), Update() or SaveOrUpdate() functions on objects that are not in a session, hibernate execute the sql statements appropriate for the command, no matter if the objects really have changed or not.

Thanks! I resolved by setting all log information on debug level on log4net and it turned out that since I inhherit every entity on BaseEntiy and in base entity I had property for last updated user, that got user name from static value.

If I removed this everything started working fine and updates were made only for those records that realy changed.