lost SQL DB connection


  • Moderators

    I have an application writing into a table frequently. In general it does its job sufficiently and shall 24/7. In the mean time I have experienced twice a loss of connection to the DB.

    When starting to write a class to safe-keep the connection details I realized QSqlDatabase may be used to retrieve the essential information and reopen.
    The error message received is:

    MySQL server has gone away QMYSQL: Unable to execute query
    

    In order to prevent the problem for happening again I plan to setup up a handler. I am wondering now if a simple open to the DB shall be enough?
    But on the other hand this could be already handled internally.

    In the doucmentation I could find anything explaining the suituation. Did I run into a very uncommon problem?

    Restarting the application again was sufficient to cure the problem. Therefore, I do not expect an external DB problem.



  • Hi,
    there is probably some kind of auto-disconnect by the DB after a maximum connection time or timeout after last write or read.
    -Michael.


  • Qt Champions 2017

    The error message "MySQL server has gone away QMYSQL: Unable to execute query" gives many hits :) and as @m.sue suggests

    http://stackoverflow.com/questions/3615422/mysql-server-has-gone-away

    "By default, the server closes the connection after eight hours if nothing has happened. You can change the time limit by setting the wait_timeout variable when you start mysqld."

    http://dev.mysql.com/doc/refman/5.7/en/gone-away.html


  • Moderators

    @m-sue @mrjj thanks for your replies.

    The stackoverflow link provides also the treatment. Looks a bit "wooden" ;)


  • Qt Champions 2017

    @koahnig
    Well the "MySQL server has gone away" msg also seems slightly "wooden" so it fits perfectly :)


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