Comment 4 for bug 1481262

The situation can be even worse with the usage-list call (all tenant),
it can permanently grow the memory allocated by the n-api processes by a huge extend (multiple Gigabytes, each worker).

1. The aggregation should be done on the DB side.
2. n-api should not ever to fetch more then osapi_max_limit of things ever.
3. some these statics should be handled by the telemetry service or depending on service which consuming the telemetry data, instead of having nova to this job.