[ZODB-Dev] session problems

[Jim Fulton]

Florent Guillaume wrote:
> Ok I've dug deeper and now understand the problem.

Thanks for the great detective work!

 > The root cause is  in the multi-databases support.

Or the misuse thereof. :)

> The problem is that the Zope startup only closes the main connection  it 
> had on the root database. The first connection to the  TemporaryStorage, 
> created and opened during Zope startup, is never  closed, so still is a 
> synchronizer in its original transaction, but  is nevertheless reused in 
> other transactins, without a proper  synchronizer set up.
> 
> When a MountedObject needs to be traversed, it tries to find an  
> existing connection for the new database by doing:
>     conn = anyjar.get_connection(db_name)
> where anyjar is the "parent" connection. If there's a linked  connection 
> for that database, it's returned, otherwise if the multi- database 
> already has seen the wanted database, it opens a connection  from it, 
> then adds it to the "linked" connections attribute  (conn.connections) 
> and shares this attribute between the two  connections.
> 
> I that fails, because the connection has never been linked to the new  
> database (which is the case during startup code), then the  
> MountedObject code does:
>     conn = self._getDB().open()
> Here _getDB() correctly returns a newly instanciated database, which  
> has been linked to the other ones in the multi-databases setup  (shared 
> "databases" dictionnary attribute, ultimately coming from  
> Zope2.Startup.datatypes.DBTab.databases).
> 
> Then open() returns a new opened connection for that database. *BUT*  
> this new connection is not "linked" to the others (using  their 
> .connections attribute).

I don't understand why the temporary database isn't part of the multi-database
to begin with.  The mounting code should absolutely not try to open the database
connection itself.  It should call get_connection on an existing connection
and fail if that fails.

Jim

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