[ZODB-Dev] ConflictError Programming Recipe Required

[Kevin Gill]

Today, during an important task, the page I was loading raised 
ZODB.POSException.ConflictError.

It appears that the Zope system, being quite sensible tried the page three 
more times before returning the exception to me. I cannot reproduce the 
exception and the next time I ran the same page it did not occur.

This was extremely embarassing for me. The page in question was to send an 
email and text message to 150 people. Instead they now have received 5 texts 
/ emails each. [ 5 = original + 3 retries + second attempt ].

Clearly, the fault is my own. I should not have built a transaction which is 
reversable which has the side effect of sending emails / texts. 

I am looking for advice in how to program this type of problem, a recipe if 
you like.


There seems to me to be a number of theoretical options....

1.	commit after each email / text message 
2.	run a second thread where the first thread updates the database and the 
second database sends the emails / text messages
3.	Trap the error and resolve it


However, these all seem to have problems (to me)....

1.	I cannot seem to end the transaction and start a new-one while serving a 
single page (and if I could, I am not sure that it would be sensible).

2.	This simply transfers the same problem onto a second thread. The second 
thread is less visible and will reduce the maintainability ./ stability of 
the solution.

3.	I believe that it cannot be resolved. It occurred during a commit().


QUESTION : WHAT RECIPIES DO YOU USE IN A SITUATION LIKE THIS?

Thanks

Kevin




For the enthuastic here is my Zope Info....

Zope 2.6.1
Linux: Debian Woody
Database: Postgres

And my traceback ....
Site Error
An error was encountered while publishing this resource.

ZODB.POSException.ConflictError

Sorry, a site error occurred.

Traceback (innermost last):

Module ZPublisher.Publish, line 150, in publish_module
Module ZPublisher.Publish, line 127, in publish
Module ZPublisher.Publish, line 127, in publish
Module ZPublisher.Publish, line 127, in publish
Module ZPublisher.Publish, line 122, in publish
Module Zope.App.startup, line 142, in zpublisher_exception_hook
Module ZPublisher.Publish, line 102, in publish
Module Zope.App.startup, line 200, in commit
Module ZODB.Transaction, line 235, in commit
Module ZODB.Transaction, line 349, in _commit_objects
Module ZODB.Connection, line 391, in commit
__traceback_info__: (('BTrees._IOBTree', 'IOBucket'),
'\x00\x00\x00\x00\x00\x00\x03\xaa', '')
Module Products.TemporaryFolder.TemporaryStorage, line 134, in store
ConflictError: database conflict error (oid 00000000000003aa, serial was
0350f384964c1baa, now 0350f38180f99a44)