Could folks have a look and tell me what they think of the proposed patch? Actually it is my belief this is a concern of DB or Connection, not MountedObject, and the code shouldn't be in MountedObject but that's the easiest workaround for now.


Florent Guillaume wrote:
Ok I've dug deeper and now understand the problem. The root cause is in the multi-databases support.

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). This code from get_connections is needed:
            new_con.connections = self.connections
which would be written, in the context of code executing in MountedObject (in _getMountedConnection):
        except KeyError:
            conn = self._getDB().open()
            conn.connections = anyjar.connections
        return conn
But of course really this code doesn't belong to MountedObject. This is just the simplest way I could find, if others want to test it.

The ".connections" sharing is really funky, apparently all the connections opened in the context of the same multi-databases support are intended to be present in it. Why is this access not indirected through the multi-databases support in DB itself? Also I don't understand why open()'s "delegate" attribute is not stored as a connection attribute, and close() should reuse it instead of obeying a "primary" attribute. Anyway, I guess historical code, etc.

I'll let specialistst of the multi-databases decide what to do :)


Florent Guillaume, Nuxeo (Paris, France)   Director of R&D
+33 1 40 33 71 59   [EMAIL PROTECTED]
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