[Interest] Long running application with database connection

[Marc Schmitzer]

On 10/09/2013 12:27 PM, Marc Schmitzer wrote:
> While this works well most of the time, we occasionally have queries
> fail with "MySQL server has gone away" errors. We know that the mysqld
> process has indeed *not* gone away, and re-opening the connection works.

Ok, this appears to be caused by the wait_timeout option of the MySQL
server[1], which defaults to 8 hours.

If you are unwilling/unable to change the server config, there are at
least two ways of working around this:

1) Setting the "reconnect" option on the mysql connection.
Unfortunately, this is not supported by the Qt-API (not even
QSqlDatabase::setConnectOptions) and requires fetching the raw MYSQL*
handle from the QSqlDriver and using mysql_options() from libmysqlclient.

2) Since the wait_timeout is an *idle* timeout, the connection can
presumably be kept alive by making regular dummy queries.


[1]
http://dev.mysql.com/doc/refman/5.0/en/server-system-variables.html#sysvar_wait_timeout

-- 
Mit freundlichen Gruessen / Best regards

Marc Schmitzer

SW-Entwicklung ESWL / ESWT
Software development ESWL / ESWT

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