[Zope] db2: accumulating connections

Hi, We've got a db2 database which we access with zope. It seems that the Zope-server is regularly opening new connections but never closing them. I've already looked into the database-adapter, but to me it looks ok. Maybe somebody can explain to me how Zope works in this respect or tell me where I can find documentation? When is Zope supposed to open a new connection? When will it close an open connection? What classes are involved? Thanks for any feedback, Stephan