In message <1357350203.18.0.396444462484.issue2550731@psf.upfronthosting.co.za>
 <1357350203.18.0.396444462484.issue2550731@psf.upfronthosting.co.za>,
Bernhard Reiter writes:
>Looks like this needs some better locking during the transaction:
>Once you read with the intention to update, you need to block other processes 
>with the same goal.

This explains the observation that the problem doesn't happen with
sqlite or bsddb back ends right? Their nature serializes the database
access, so there is an implicit lock that prevents multiple processes
from opening the database in update mode at the same time.

-- rouilj