[Zope] server slowed down to a crawl

[Ben Bartrum]

> Have you found out why it is slowing?
> Has your traffic increased -> limit your traffic temporarily
> Perhaps its the Hardware? If you mean with 'old' P3/P4, perhaps
> the CPU cooler is dead and the CPU is in reduced performance mode?
> Perhaps some IO controller (disks?) is failing.
> 
> Or your changes weren't cosmetic. Roll back to your last known good
> backup (you have one, right?) and apply cour changes a atomic as
> possible and test them

Bryan Sullivan's suggestion of the DeadlockDebugger helped me to solve the problem.  The DeadlockDebugger was crucial, and far easier
to work with than I anticipated. It was quite a subtle problem - an earlier change worked fine at the time, but the deadlock started  when the underlying SQL data changed.  That is, an SQL query returned less results than the code was meant to work with, and there was no clause in a  Python script to deal with this eventuality.  So rolling back to dates when the site worked fine did not help until I understood the nature of the problem.