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MetricUnit class should be introduced. The following units It should be specified in the enumpossible to acquire the following instances:

• NUMBER - – number of times something happened or number of elements. No specific units are assigned to this value.
  Example: io.dataregion.PagesReplaced 
• NANOSECONDS, MILLISECONDS, SECONDS – for time periods.
  Example: tx.totalNodeSystemTime 
• TIMESTAMP – for specific moment in time.
  Example: cache.RebalanceStartTime 
• BYTES, KILOBYTES, MEGABYTES – for amount of data.
  Example: cache.TotalRebalancedBytes 
• PERCENT – fraction.
  Example: sys.CpuLoad 

It should also be possible to represent units like "bytes per second" and "number of times per second". A method MetricUnit.per(...)  should be implemented that will create an instance of a new MetricUnit corresponding to the ratio.

Example metrics: io.dataregion.PagesReplaceRate, cache.RebalancingBytesRate.

Risks and Assumptions

// Describe project risks, such as API or binary compatibility issues, major protocol changes, etc.

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