Dieter Maurer wrote:
Jim Washington wrote at 2005-12-13 21:40 -0500:
...
Now, looking closer at the code, a ping like this might be not too bad,
because isConnected() is only called when a connection is requested, not
for every SQL statement executed. So, it might not be so onerous as
originally thought. Still not ideal, though.
Be careful what you do when you find that "isConnected()" returns false.
Note, that, in general, it would be a bug to just reopen a new connection
in this case: previous operations against the connection might have
been lost without notice when you simply reopen a new connection
and do as if nothing bad had happened.
Instead, you should reopen the connection and then raise an exception
similar to "ZODB.POSException.ConflictError". Hopefully, the publisher
will handle this kind of exception correctly (by retrying the complete
request).
Thanks, Dieter.
The situation I wish to handle is the case where MySQL server silently
closes its connection with Zope after 8 hours idle, which likely will
happen at least once a day.
What seems to work for me now is the following as
mysqldbda.adapter.MySQLdbAdapter.isConnected()
def isConnected(self):
try:
self._v_connection.ping()
except:
# not connected or ping did not restore MySQL connection
if self._v_connection is not None:
self._v_connection.close()
self._v_connection = None
return False
return True
I am not well-versed in the intricacies of conflictError, so what else
should happen here? I do not see how there would be unresolved
transactions remaining, and the connection I need is now available or
soon will be established.
In the current rdb implementation, isConnected() is not called for each
SQL statement. It is only called when the utility is called.
e.g.,
conn = zapi.getUtility(IZopeDatabaseAdapter, 'spam') #isConnected has
not been called yet
db = conn() #here, isConnected() gets called
c = db.cursor() #isConnected() is not called
c.execute('SELECT 1') #isConnected() is not called
-Jim Washington
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