We have some software which sits behind our version control repository
and which notifies roundup via the email gateway when certain kinds of
commits have been made.  It is frequently the case that several of these
emails are sent out in quick succession (as this process is automated)

Recently, we've been getting error messages of this sort:
An unexpected error occurred during the processing                     
                                                                     
of your message. The tracker administrator is being                    
                                                                     
notified.                                                              
                                                                     
                                                                       
                                                                     
----------------                                                       
                                                                     
Traceback (most recent call last):                                     
                                                                     
  File "/usr/lib/pymodules/python2.5/roundup/mailgw.py", line 738, in
handle_Message                                                         
    return self.handle_message(message)                                
                                                                     
  File "/usr/lib/pymodules/python2.5/roundup/mailgw.py", line 794, in
handle_message                                                         
    return self._handle_message (message)                              
                                                                     
  File "/usr/lib/pymodules/python2.5/roundup/mailgw.py", line 1369, in
_handle_message                                                       
    cl.set(nodeid, **props)                                            
                                                                     
  File "/usr/lib/pymodules/python2.5/roundup/backends/rdbms_common.py",
line 1606, in set                                                    
    propvalues = self.set_inner(nodeid, **propvalues)                  
                                                                     
  File "/usr/lib/pymodules/python2.5/roundup/backends/rdbms_common.py",
line 1816, in set_inner                                              
    self.db.setnode(self.classname, nodeid, propvalues,
multilink_changes)                                                     
             
  File "/usr/lib/pymodules/python2.5/roundup/backends/rdbms_common.py",
line 933, in setnode                                                 
    self.sql(sql, vals)                                                
                                                                     
  File "/usr/lib/pymodules/python2.5/roundup/backends/rdbms_common.py",
line 159, in sql                                                     
    self.cursor.execute(sql, args)                                     
                                                                     
ProgrammingError: ERROR:  could not serialize access due to concurrent
update                                                                
                                                                       
                                                                     
update _issue set _activity='2010-10-15
13:14:44.653',_actor=1837,_resolvedin=2,_status=8 where id=1942 

Strangely it seems that the change we want to make takes effect anyway.

See also http://bugs.darcs.net and the attached mail that our
auto-updater tries to send