If you enabled BCT.
Doc:
KRC : Recovery Block Change Tracking (krc)
KRC_CHANGES : Recovery Block Change Tracking CHANGES ((null))
KRB_TRACE : Set krb trace options
KRB : Kernel Backup Restore (krb)
KRB_THREAD KRBBPC Thread Switches ((null))
KRB_IO KRB I/O ((null))
KRB_INCR KRB Incremental Restore ((null))
KRB_PERF KRB Performance Tracing ((null))
KRB_BPOUTPUT Detailed Backup Piece Output ((null))
KRB_BPVAL Detailed Block List During Restore Validate ((null))
KRB_FLWRES Details on Restore Flow ((null))
KRB_FLWCPY Details on krbydd Flow ((null))
KRB_FLWBCK Details on Backup Flow ((null))
KRB_FLWUSAGE RMAN Feature Usage ((null))
KRB_OPTIM Unused Space Compression ((null))
Commands:
alter system set events ‘TRACE[krb.*] disk=highest, memory=highest’;
alter system set events ‘TRACE[krc.*] disk=highest, memory=highest’;