[Zope-DB] ZPsycopgDA (version 1.0.13) problems

[Dieter Maurer]

Dear Michele and Federico,

we are using your ZPsycopgDA (1.0.13) and encountered the following
problems:

  *  "db.DA.query" catches "psycopg.ProgrammingError" and
     checks against "ERROR:  Can't serialize access due to concurrent update".

     However, our Postgres intallation reports this problem as
     "psycopg.IntegrityError".

     I suggest to add that in the "except" clause:

       except (psycopg.ProgrammingError,psycopg.IntegrityError), perr:


  *  The code uses "raise sys.exc_type, ...". However, this is
     not thread safe. Suggest to use "raise" instead.

  *  The error handling in "db.DA.query" is inhomogenous (and irrational):

      - "InterfaceError" checks for "self.db" which is unnecessary,
        because we just used it (therefore it must exist).

      - "OperationalError" does not check for "self.db" but wraps
        the close/reopen in a redundant "try: ... except: raise".

     Suggest to fold and unify handling for "OperationalError" and
     "InterfaceError":

       except (psycopg.OperationalError, psycopg.InterfaceError), err:
           del c; del self.db # close
	   self.db= self.connect(self.connection) # reopen
	   return self.query(query_string,max_rows) # retry

  *  "max_rows==0" is interpreted as to not return results at all.
     It seems more consistent with other use of the value "0"
     to interpret it as "no restriction"

  *  I have added error logging to "db.DA.query" such that one can better
     understand what goes wrong.

  *  I have been unable to understand the motivation for the "failure"
     use in "db.DA.query".


Besides, we still have a problem not yet understood:

   Sometimes, we seem to get empty result sets from Postgres (where we know,
   the result set should be non-empty).
   We are still investigating this problem.
    


Kind regards
Dieter