Re: how to get rid of BTreeContainer as global variable

I am not using any connection. I just want a store to have large mapping in 
RAM. I chose BTreeContainer. I want to replace it with some non-persistent 
alternative class.

On Wednesday, 7 September 2016 17:58:09 UTC+5:30, Jason Madden wrote:
>
>
> > On Sep 7, 2016, at 06:56, Sanjay Rao <[email protected] <javascript:>> 
> wrote: 
> > 
> > Hi, 
> > 
> > I am using multiple objects of BTreeContainer 
> (zope.app.container.btree.BTreeContainer) to store global mapping data in 
> my application. 
>
> (Note that the code has moved to simply 
> zope.container.btree.BTreeContainer. The zope.app.container.btree name is 
> simply a backwards compatibility alias, new code should use 
> zope.container.btree directly.) 
>
> > Now with new ZODB(4.4) and ZEO(4.3),  my application randomly throws 
> following Error 
> > 
> > ConnectionStateError: Shouldn't load state for 
> baton.tpd.variants.VariantsRegistry 0x043155 when the connection is closed 
> > 
> > 
> > If I replace BTreeContainer with OOBTree, Is it a safe bet to get rid of 
> this problem ? 
>
> No. They're both persistent object types. 
>
> This problem occurs when using *any* persistent object outside the scope 
> of its connection. This was discussed in some detail in an email on Aug 24: 
>
> > Note, however, that that connection is not necessarily safe to use or 
> associated with the current thread. If you have a bug in your code that 
> allows a persistent object to leak between threads or outlive a transaction 
> boundary when the connection is closed, you can run into trouble. A faulty 
> cache, for example, can produce this situation, leaving you with 
> ConnectionStateErrors: 
> > 
> > py>> import ZODB, ZODB.DemoStorage, persistent, transaction 
> > py>> db = ZODB.DB(ZODB.DemoStorage.DemoStorage()) 
> > py>> conn = db.open() 
> > py>> plist = persistent.list.PersistentList() 
> > py>> conn.root()['key'] = plist 
> > # Note that there is no connection yet 
> > py>> plist._p_jar 
> > # After commit we have a connection 
> > py>> transaction.commit() 
> > py>> plist._p_jar 
> > <Connection at 10728bf30> 
> > # But we still have it after the connection is closed 
> > py>> conn.close() 
> > py>> plist._p_jar 
> > <Connection at 10728bf30> 
> > # And it is useless 
> > py>> plist.thing 
> > Traceback (most recent call last): 
> >   ... 
> > ConnectionStateError: Shouldn't load state for 
> persistent.list.PersistentList 0x316490b7e11981b6 when the connection is 
> closed 
> > py>> plist._p_jar.root() 
> > Traceback (most recent call last): 
> >   ... 
> > ConnectionStateError: The database connection is closed 
> > 
> > So I guess I'm just saying, be careful about the lifetime of your 
> persistent objects. 
>
> Other than a faulty cache, trying to use persistent objects as module 
> globals, or passing them up through WSGI middleware or pyramid tweens that 
> are "above" the connection/transaction management can cause this type of 
> error. 
>
> I think you'll find that the error isn't really "random," there's a 
> specific misuse of objects that gets you there. 
>
> Jason

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