Is WindowedCount the right stat type to use in MetricsResourceMethodApplicationListener?

[ericwush]

By default, an application is configured to keep two samples in a SampledStat, e.g., WindowedCount, each sample maintains a 30-second window. Typically, metrics are exposed by JmxReporter. When the value of an MBean is being retrieved, it calls the stat's measure method. In WindowedCount, measure simply combines all data points in all (two) samples to get the sum. Unless the MBean retrievals are well aligned with the start of a window with the intervals being (window size * # of samples), I don't see how it could report the right count.

For instance:
T: 0----5----[10]----15----[20]----25----[30]
W: |-----1-----|------2------|------3-------|

Let's assume the window size is 10, the metrics get collected every 10 seconds.
Collection 1 at 15: it returns the sum of (full window 1 and half of window 2), i.e., 0-15
Collection 2 at 25: it returns the sum of (full window 2 and half of window 3), i.e., 10-25
In this example, the values between 10-15 are repeatedly reported.

Can anyone please verify if this is the right understanding?

[ehumber]

@splett2 Any thoughts on the question from Eric?

[splett2]

seems reasonable to me. WindowedCount in the kafka code base is usually used as a rate stat in combination with a cumulative count (the count) to construct a meter.

I would probably rename the existing CumulativeCount to request-rate and then the new cumulative count metric to request-total.

[ericwush]

Thanks @splett2. I will rename it to request-total and leave the existing ones to code owner to change because we need to make sure anyone using those metrics for alerts should be notified.

[splett2]

@ehumber
we should probably just deprecate and eventually remove the existing request-count metric. AFAIK it should express an equivalent value to the request-rate metric, since both are using a WindowedCount as the underlying Stat.

[ericwush]

Another approach is rely on request-total and calculate the rate in dd? That is something I am going to try.

Also, response-byte-rate and response-size-avg are duplicate too?

[dimitarndimitrov]

CC @rigelbm