[mod_python] question about global_lock and global_unlock

[Bram Van Steenlandt]

Hi,

What is the point of _apache._global_lock and _apache._global_unlock ?

I've found and SQL session online for mod_python, I'm using this with 
postgresql.
The load function is:
     def do_load(self):
         _apache._global_lock(self._req.server, None, 0)

         c = self._db.cursor()
         c.execute("""SELECT %s
                      FROM %s
                      WHERE %s = %s
                      """ % ( 
self._val_colname,self._table,self._key_colname,"%s"),[self._sid,] )
                      # txt2db keeps this safe, so that a sid
                      # cannot be constructed to alter the
                      # query

         r = c.fetchone()
         try:
           if r:
             return cPickle.loads(r[0])
           else:
             return None
         finally:
           _apache._global_unlock(self._req.server, None, 0)

It's unclear to me why this global lock is needed, isn't this a serious 
limitation on performance ?
I would assume at least do_load can do without is as there is no real 
problem when you would do this simultanious.
I would think only insert and update require a lock, even update/save 
could do without one I think (insert would be dangerous as it could 
create two records).
Is this indeed not needed and most likely copied from a session type 
where you had to be carefull about opening the same file twice ?

Can anyone shed some light on this ?

thx
Bram