Server error 500 while processing your request:
SQL error: ERROR:  could not serialize access due to concurrent update

delete from mediator_system_session where expires < 'now'
while executing query  delete from mediator_system_session where expires < 'now'

Traceback (most recent call last):
  File "/usr/local/lib/python2.5/site-packages/mediator/servlet/mod_python3.py", line 207, in do
    self.server.atRequestDone(self)
  File "./core/request.py", line 60, in atRequestDone
  File "./core/sessions.py", line 188, in _storeSession
  File "./core/sessions.py", line 136, in store
  File "./core/sqldbi.py", line 143, in execute
RuntimeError: SQL error: ERROR:  could not serialize access due to concurrent update

delete from mediator_system_session where expires < 'now'
while executing query  delete from mediator_system_session where expires < 'now'