cayenne tomcat memory management

[Emanuele Maiarelli]

I'm using cayenne 3 with tomcat, and im getting context by this way
..
DataContext dc= ServletUtil.getSessionContext(sess)
...
using httpsessioncontext.
To ensure session to be closed i implemented logout from session  by 
calling

...
  <%session.invalidate();%>
...


But after many sessions opened, i step into memory lacks even if 
application retrive few data from database.

Any hint?

PS: i tried to use  getThreadObjectContext but was unable to do it. Any 
example about using ThreadObjectContext?