This error message may
appear in the alert log file of standby database after an upgrade/PSU etc. is
applied on the primary database and if real time apply is enabled on the
standby database.
The procedure to apply a PSU
or other (rolling) patches is that it is first applied on the standby database
server and after that on the primary database, and any post patch (or upgrade)
scripts are executed on the primary database. Once this completes, all database
changes happened during patch/upgrade scripts execution are shipped through
redo logs to the standby database and standby database eventually becomes in
sync with the primary.
