[Zope] Problem with AdManager

[David]

Hi

Setup is: Zope 2.7.5, Python 2.3.5 (UNIX/gcc 2.95) (No ZEO, no CMF, no 
Plone!)

We are trying to use the AdManager ZClass, a great product doing 
exactly what we needed.

Testing this on the developer's machine, we had no problems. But having 
now done a "small scale" stress testing (requesting about 20 pages per 
second) on the server, some pages suddenly throw errors of the 
following kind (see traceback below). The errors are not all 100% like 
this one, but similar enough, I guess. The errors occur on a ratio of 
about 1:4 (so 4 successful pages, then one error). [I know this is not 
really scientific or would stand in a statistical analysis, but just to 
give you an idea.] We could also not find any connection between the 
errors and any of the 5 banners we're using for testing. (The product 
rotates which banner is displayed.)

-- from the traceback --
ZODB.POSException.ReadConflictError

Sorry, a site error occurred.
Traceback (innermost last):

Module ZPublisher.Publish, line 175, in publish_module_standard
Module ZPublisher.Publish, line 149, in publish
Module ZPublisher.Publish, line 149, in publish
Module ZPublisher.Publish, line 149, in publish
Module ZPublisher.Publish, line 139, in publish
Module Zope.App.startup, line 163, in zpublisher_exception_hook
Module ZPublisher.Publish, line 101, in publish
Module ZPublisher.mapply, line 88, in mapply
Module ZPublisher.Publish, line 39, in call_object
Module OFS.DTMLMethod, line 144, in __call__
Module DocumentTemplate.DT_String, line 474, in __call__
Module DocumentTemplate.DT_Var, line 214, in render
Module OFS.DTMLMethod, line 137, in __call__
Module DocumentTemplate.DT_String, line 474, in __call__
Module DocumentTemplate.DT_Var, line 214, in render
Module OFS.DTMLMethod, line 137, in __call__
<DTMLMethod instance at 91a9b90>
URL: /advert_chooser/manage_main
Physical Path:/advert_chooser
Module DocumentTemplate.DT_String, line 474, in __call__
Module DocumentTemplate.DT_With, line 76, in render
Module OFS.DTMLMethod, line 137, in __call__
<DTMLMethod instance at 9281cb0>
URL: /site/advertisements/show_banner/manage_main
Physical Path:/site/advertisements/show_banner
Module DocumentTemplate.DT_String, line 474, in __call__
Module DocumentTemplate.DT_With, line 76, in render
Module DocumentTemplate.DT_In, line 703, in renderwob
Module DocumentTemplate.DT_Util, line 192, in eval
__traceback_info__: date_end
Module ZODB.Connection, line 599, in setstate
Module ZODB.Connection, line 628, in _is_invalidated
ReadConflictError: database read conflict error (oid 0x3244, class 
*ilYYN6piu7CmJucspzx0gA==.AdBanner)

-- end traceback --

Any idea what is happening here?? This is beyond my understanding of 
Zope/ZODB and as it only happens occasionally, it does not seem to be a 
straight bug.
Any suggestions on what I could try would be very welcomed.
(If you are using a Banner Ad Manager that is a proper product, not a 
ZClass, that runs on a plain Zope, let me know.)

Thanks in advance,

DR