Hi Christian,
thank you for your help.
As I already wrote: When I execute the Checkmk agent locally on the affected server (using check_mk_agent.exe test), the plugin is executed properly. I get all Oracle sections and their values. So I guess, that there is no database problem.
Indeed, there can be a relation to backups, because the Check_MK Discovery shows vanished services always late in the evening and at the weekend. I will investigate.
But how can I avoid that a backup effects the agent requests? Shall I set a scheduled downtime?
Kind regards,
Antje