On Thursday 28 December 2006 20:36, Oleg Broytmann wrote:
> On Thu, Dec 28, 2006 at 06:56:08PM +0100, Markus Gritsch wrote:
> > Since there was no comment on the e-mail below, I resend it in case
> > it got lost.
>
> Sorry for the silence. I have got it the first time. Just don't have
> time to work on it. There are other patches to test; I am working on
> the patch that implements delColumn and fromDatabase for SQLite.
> Regarding the patch. I think to fix the problem I will replace
> "while 1" with "for i in range(1000): sleep(1)". There should be no
> "raise", or the loop would be meaningless at all. The idea of the loop
> is to wait until the server is restarted.
I disagree with you here. It's a bad design to let SQLObject (a library)
make this decision (what to do and how long to wait when a connection is
lost and cannot be reestablished).
I agree that SQLObject should attempt to reconnect, for cases where the
server was restarted or the connection was lost because it was idle too
long. But if it can't reconnect immediately it should signal this error
to the caller (application). This reconnect is only to avoid extra hassle
in the application for something that can be done automatically and takes
no extra time.
Trying to reconnect forever or for long periods of time is a bad thing.
Just imagine the scenario where I have a realtime application using
sqlobject and a replicated master-slave database. If the master dies, or
is taken out for maintenance, I want the application to commute to the
slave database as quickly as possible (as soon as it finds out that the
connection was lost). With the original code or your proposal I cannot do
this and my application will block waiting for sqlobject to do something
it cannot do because it has no knowledge of the situation or what the
application intends to do in such cases.
Attached is a patch that fixes this in a better way. It still allows
reconnects if the database connection was lost because of a server
restart or the connection being closed because it was idle too long, but
will allow the application to make decisions on its own if the database
is down for good and cannot be reconnected.
--
Dan
Index: mysqlconnection.py
===================================================================
--- mysqlconnection.py (revision 2165)
+++ mysqlconnection.py (working copy)
@@ -78,7 +78,19 @@
conn.autocommit(auto)
def _executeRetry(self, conn, cursor, query):
- while 1:
+ # When a server connection is lost and a query is attempted, most of
+ # the time the query will raise a SERVER_LOST exception, then at the
+ # second attempt to execute it, the mysql lib will reconnect and
+ # succeed. However is a few cases, the first attempt raises the
+ # SERVER_GONE exception, the second attempt the SERVER_LOST exception
+ # and only the third succeeds. Thus the 3 in the loop count.
+ # If it doesn't reconnect even after 3 attempts, while the database is
+ # up and running, it is because a 5.0.x (or newer) server is used
+ # which no longer permits autoreconnects by default. In their case a
+ # reconnect flag must be set when making the connection to indicate
+ # that autoreconnecting is desired and the python-mysqldb module
+ # doesn't set this flag.
+ for c in range(0, 3):
try:
if self.need_unicode:
# For MysqlDB 1.2.1 and later, we go
@@ -88,7 +100,9 @@
else:
return cursor.execute(query)
except MySQLdb.OperationalError, e:
- if e.args[0] == 2013: # SERVER_LOST error
+ if e.args[0] in (2006, 2013): # SERVER_GONE or SERVER_LOST error
+ if c == 2:
+ raise OperationalError(ErrorMessage(e))
if self.debug:
self.printDebug(conn, str(e), 'ERROR')
else:
-------------------------------------------------------------------------
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