In addition to what Dieter said (thanks, Dieter!),
> Trough 'slave' I only do read operations at the moment.
You didn't say which version of ZODB you're using. If it's a version before
3.3, then a client that doesn't modify objects may not process invalidations
even when you cross a transaction boundary. Much has been written about
that before, so I'll just point you at an earlier thread:
For more information about ZODB, see the ZODB Wiki:
ZODB-Dev mailing list - ZODB-Dev@zope.org