Dropping network connection leads app to freeze if a remote db is open

[Mark81]

Qt 6.4.0 on Ubuntu 22.04.
I open a remote odbc connection:

bool OdbcSql::connectToDB(QUrl host, QString database, QString username, QString password)
{
    _host = host;
    _database = database;
    _username = username;
    _password = password;

    qInfo() << ID << "Trying to open database...";
    _db.setDatabaseName(QStringLiteral("Driver=/opt/microsoft/msodbcsql18/lib64/libmsodbcsql-18.2.so.1.1; Server=%1;Database=%2; Encrypt=No;").arg(host.url()).arg(database));
    _db.setUserName(username);
    _db.setPassword(password);
    _db.setConnectOptions("SQL_ATTR_CONNECTION_TIMEOUT=5;SQL_ATTR_LOGIN_TIMEOUT=5");

    bool ret = _db.open();
    if (ret) qInfo() << ID << "Database opened successfully";
    else qWarning() << ID << "Database opening failed:" << _db.lastError();

    return ret;
}

After a connection I try to simulate a network issue rejecting all traffic from/to the host using ufw. The whole application freezes forever (at least for over 5 minutes) in the QSqlQuery::exec() call:

bool OdbcSql::retrieveNewOrders()
{
    QString sql = QString("SELECT * FROM %1 WHERE mo_rilasciato='N' ORDER BY td_datord, td_numord;").arg(TABLE_NEW_ORDERS);
    QSqlQuery query(_db);

    if (!query.prepare(sql))
    {
        qWarning() << ID << "Prepare query failed" << sql;
        qWarning() << ID << query.lastError();
        return false;
    }

    query.exec(); // <----- IT NEVER RETURNS
    while (query.next())
    {
        if (query.isValid())
        {
            bool ret = _ordersDB->enqueueNewOrder(query.record());
            if (ret) setOrderProcessed(query.record(), true);
        }
    }

    return true;
}

How should I handle such a behavior?
It never exits from that function, hence I can't even check the properties of the database.

[zeljko]

@Mark81 see sysctl net.ipv4.tcp_keepalive_time, you should reduce it to something reasonable for you (7200 secs is default afair).