refresh rate for Performance Manager

[hmadadian]

hi I tried the "vm_perf_example.py" in the pyvmomi-community-samples, and it was okay, but there are two problems: in some time periods it just returns an array of null just like below: (vim.PerformanceManager.EntityMetricBase) [ (vim.PerformanceManager.EntityMetric) { dynamicType = <unset>, dynamicProperty = (vmodl.DynamicProperty) [], entity = 'vim.VirtualMachine:vm-2619', sampleInfo = (vim.PerformanceManager.SampleInfo) [], value = (vim.PerformanceManager.MetricSeries) [] } ] and the other problem, it returns data in periods of 300s (5 minutes)! how can we set refresh rate to something like 30s