Re: [Modeling-users] Warning: possible problem with Zope, maybe MT-related

[Sebastien B. <sbi...@us...>]

        Hi,

>   Just a quick note to warn you about the fact that I currently have a
>   very annoying bug revealing itself on a zope-based application using
>   the modeling.
>=20
>   It is still not clear where the bug is, but it has been reported
>   that it was also observed with zope and ZPsycopgDA alone.
>=20
> It might be a MT-issue, or just a Zope-issue (this is just my guess at
> this point).
>=20
>   Description of the problem: at some point, the psycopg adaptor stops
>   adding BEGIN and END or ABORT at the begin/end of the txn.  From
>   that point, none of the sql statements sent to the pg server is
>   committed anymore, hence they are lost.

It seems that the problem is triggered when the same psycopg cursor is
used in two different threads.

  I submitted and fixed bug #699272 for the modeling framework: when
  calling EditingContext.objectsCountWithFetchSpecification() the
  underlying adaptorChannel was not closed at the end. Hence, even if
  MDL_PERMANENT_DB_CONNECTION was unset, the corresponding
  (psycopg-)connection to the database was not closed. This makes it
  possible for the same cursor to be reused by an other request,
  especially in a different thread (when used within zope e.g.) and as a
  consequence it made the bug more likely to occur.

--> If you are using the framework in a MT environment, please update
--> your copy of DatabaseChannel w/ v.1.10 or apply the patch attached
--> below. Additionally, please remember that you are strongly advised
--> against setting MDL_PERMANENT_DB_CONNECTION in a multi-threaded
--> environment.

  This does not guarantee that the problem won't show up, but it will
  dramatically reduce its frequency. Hopefully a complete resolution for
  the bug will be found, I'll keep you informed.

        Regards,

-- S=E9bastien.



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<     $Id: DatabaseChannel.py,v 1.9 2003/02/20 11:59:52 sbigaret Exp $
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>     $Id: DatabaseChannel.py,v 1.10 2003/03/07 09:27:18 sbigaret Exp $
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< __version__=3D'$Revision: 1.9 $'[11:-2]
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<       self.__isFetchInProgress=3D0
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>       self.cancelFetch()
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