sysman.mgmt$metric_hourly

When I gather the storage cell memory utilization figures from sysman.mgmt$metric_hourly, I get a “percent used” value for “memory utilization”.

 

What is this metric actually measuring? 

Does it measure the percent used of total OS memory (OS_TOT) on the storage cell? 

Or, does it measure the percent used of the Exadata software max memory limit (CL_MAX, which is 5gb less than total memory on the storage cell)?

Or …. Does it measure something else?