key error with monitor-data

Sometimes there is a duplicateed key error when the monitor tries to save its data.

To avoid this, we can

1. delete the key (not so good, because then we have no key for the table ;-)
2. use update into instead of insert into. this statement executes the record if there is another one with the same key
3. if 2) will not help, we can maybe change the index from unique to index only