Gets server performance metrics
[mode - quicky]
perf_monitor - Returns internal data, in a structure.
simple_load - Returns an integer value that is computed
from the state of the server's internal
queues. Indicates the overall server load.
prev_req_time - Returns the time, in milliseconds, that it
took the server to process the previous
avg_req_time - Returns the average time, in milliseconds,
that it takes the server to process a
getMetricData(mode) → returns any