Oracle agent fails to come online and monitor Oracle instance if threaded_execution parameter is set to true (3644425)

In Oracle Database 12c or later, the threaded execution feature is enabled. The multithreaded Oracle Database model lets Oracle processes execute as operating system threads in separate address spaces. If Oracle Database 12c or later is installed, the database runs in the process mode. If you set a parameter to run the database in the threaded mode, only some background processes on UNIX and Linux run with each process containing one thread. The remaining Oracle processes run as threads within those processes.

When you enable the threaded_execution parameter, the Oracle agent cannot check the smon (mandatory process check) and the lgwr (optional process check) processes. These processes where traditionally used for monitoring, and they now run as threads.

Workaround: Disable the threaded execution feature, because it is not supported on Oracle Database 12c or later.