[Zope-dev] volatile state maintenance

[Itamar Shtull-Trauring]

Sam Gendler wrote:
> 
> I have a product which needs to maintain a connection to a 300MB
> database file (Metakt, if you must know).  The initial connection takees
> about 3 seconds, due to the size of the file, so I wanted to make a
> product that will keep the connection open, and re-use it.

Cool - Metakit would be really useful for a lot of stuff (sessions,
caching).  Any chance for a public release?

As for your question - you can store the connection in a volatile variable
by prefixing it's name with _v_, e.g. _v_mk_connection.  You then have to
reconnect only when the object is loaded into memory from the ZODB.  You do
this in the __setstate__ method:

    def __setstate__(self, state):
        """ initialize cache when object gets unpickled from zodb """

        # if you don't do this horrible things might happen:
        Persistent.__setstate__(self, state)
        
        #create volatile variables:
        _v_mkconnection = self.mkconnect()

Check out ZCatalog for a real example.

-- 
Itamar S.T.  itamars@ibm.net