[ZODB-Dev] Old transaction records with "bad" pickle data preventing packing

[Shane Hathaway]

On 06/14/2010 01:43 AM, Jens Vagelpohl wrote:
> My question: Is there any risk associated with ignoring the failure
> during packing? The latest object versions for the persistent objects in
> question do not have the problematic attribute anymore, so the latest
> records are "safe" and will not cause the AttributeError, anyway.

In the general case, a failure to unpickle could be caused by some 
temporary condition, so we can't ignore it.  For example, a broken 
__setstate__ method could be involved.  Ignoring unpickling errors could 
cause the pack to not discover all references and possibly delete more 
objects than it should.

In your case, you have already determined that this specific pickle is 
permanently broken, so the references from it don't matter and packing 
is probably safe.  However, can you be certain that the rest of your 
database is free of temporarily broken pickles?  If I were you, I would 
add some logging to ensure the exception handler is triggered only once, 
pack, and then revert the ZODB code change.

Shane