JRTE E LockHandler: failed to lock, it might be database failure

Hi experts,

   I just found the following disturbing line in our production sm.log:

4504( 6932) 09/04/2018 11:47:26 JRTE E LockHandler: failed to lock, it might be database failure, rc=-1, lock = Key:schedule:sla, IP:<XXXXXXXXXXX>, PID:4504, TID: 6648, SID: 57, Retry: 0

   Obviously went on googling it but haven't found anything. We haven't noticed any error. Should I be worried?

BR,

Dávid