[Zope-DB] SQL Relay and _v_ variables

[Dieter Maurer]

Chris Withers wrote at 2003-10-29 11:11 +0000:
 > Dieter Maurer wrote:
 > > However, the DA must be very careful to not open a second connection
 > > to the same database within the same request. Otherwise, what
 > > should be one transaction may become several independent ones.
 > > This can lead to various obscure failures (e.g. database inconsistencies).
 > 
 > Indeed, this is why you suggested that if the connection goes away, a 
 > ConflictError of some sort should be raised, so that Zope retries the request, 
 > right?

Right.

 > Where is the code which actually does this?

Usually, it is in "query".

For "ZPsycopgDA", it (e.g.) looks like:

    "Products/ZPsycopgDA/db.py":

    def query(self, query_string, max_rows=None):
        ...
        try:
            for qs in filter(None, map(strip, split(query_string, sql_delimiter	
	    ....
        except (psycopg.OperationalError,psycopg.InterfaceError), err:
            # maybe an intermittent failure
            # close, reopen and retry
            # Python will stop us, when we try too often ("Maximal recursion"),
            #   but be aware that on some systems the C runtime stack
            #   may overflow before (in which case, the process is killed
            #   by SIGSEGV)
            del c ; del self.db
            self.db = self.connect(self.connection)
            LOG('Postgres',INFO,'Retry',query_string)
            return self.query(query_string, max_rows)
    
This code does not yet follow my advice to raise "ConflictError".

The comment is from me and not from the original authors of
"ZPsycopgDA". The code is theirs.


-- 
Dieter