[Zope] SESSION Errors

[Dennis Allison]

Accessing session variables fails occasionally--perhaps once every 10000
references or so!  (See collector issue #848 where I just added a
comment.)

Presumably this is a read conflict in temporary_folder.  The access to the 
variable uses a python script--

request=container.REQUEST
try:
    session=request['SESSION']
    return session[varname]
except KeyError:
    container.oopsSession( varname )
    raise

oopsSession() is a debug routine which reports that it cannot find
REQUEST.

This is Zope 2.6.2b3 and Python 2.1.3.  This version of Zope is patched to
NOT use the (flawed) LowConflictConnection for temporary storage.   

This is a critical bug for us and is becoming more so as our usage grows.
It's a showstopper for our users as we are entirely session based!

It's fairly likely that some internal data structure gets corrupted.  We
tend to fetch session variables in clusters, and when one fails all
subsequent ones fail.  Sad to say, the failure kills the user's session
and releases a burst of emotional energy )-:

Any suggestions for a fix or workaround?   This particular bug has been
seen in 2.7.4 so upgrading is not going to fix things.