[mythtv] mythbackend 0.22-fixes problem with duplicate database connection name

[Roger James]

I have been recently seeing a problem with mythbackend (0.22-fixes rev 
23482) reporting that the database connection had gone away and some 
(all?) database transactions being rejected with a "Driver not loaded" 
error. The common factor behind these failures seems be that they all 
start after the following QSqlDatabasePrivate messages are logged.

QSqlDatabasePrivate::removeDatabase: connection 'DBManager5' is still in 
use, all queries will cease to work.
QSqlDatabasePrivate::addDatabase: duplicate connection name 
'DBManager5', old connection removed.
2010-02-28 05:32:54.876 New DB connection, total: 6
2010-02-28 05:32:54.877 Connected to database 'mythconverg' at host: myth
2010-02-28 05:32:54.878 MSqlDatabase::OpenDatabase(), db object is not 
valid!
QSqlQuery::exec: database not open
QSqlQuery::exec: database not open
2010-02-28 05:32:54.933 Driver error was [1/-1]:
Driver not loaded
Database error was:
Driver not loaded

This leaves the backend in a confused state where it appears that some 
database transactions are failing are and I suspect some are still 
working. Subsquent new recordings appear in the new recordings list but 
but have no file associated with them. My guess is that database 
connections "DBManager0" to "DBManager4" are still working but the old 
"DBManager5" is now broken.

I do not recollect having this problem on my old single processor 
backend system. I think I have only seen it on my new quad core fast 
processor system. But I cannot be certain.

The problem usually seems to occur when the system is just idling doing 
EIT scans. But I have it occur twice when three recordings tried to 
start at the same time.

The only similar problem I can find is 
http://svn.mythtv.org/trac/ticket/7836. But this is reported as a 
frontend problem. I wonder if the same bug in MDBManager could be 
causing my problem.

Any one seen this or got any ideas what is causing it.

Roger