Phil Yang created HBASE-18151:
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Summary: Improvement on Histogram
Key: HBASE-18151
URL: https://issues.apache.org/jira/browse/HBASE-18151
Project: HBase
Issue Type: Improvement
Reporter: Phil Yang
There are some bugs and some places we can improvement in the new native
Histogram.
The default maxExpected value in HistogramImpl is Integer.MAX_VALUE << 2
(https://github.com/apache/hbase/blob/master/hbase-metrics/src/main/java/org/apache/hadoop/hbase/metrics/impl/HistogramImpl.java#L41
) which is overflow... and will be regarded as -4... And binsMax pf
FastLongHistogram will be 255(by the reason of this bug) which is too low (In
FastLongHistogram#L75 it says the expected binsMax is 1000? I think it may be
also too low. Even if there is no overflow, Integer.MAX_VALUE*4 is too large?
We may need pass the right expected min/max value when we use it because the
value may be different in scenarios. And the default value should not be 1000
or Integer.MAX_VALUE*4.
There is an assumption that the value is in uniform distribution. But if the
value is latency which is the most use case, the distribution is not uniform.
The lower the value, the higher the probability.
Because of these reasons, the 75/90/99 or other percentages may have big error
than we expected. We need find a way to reduce the error.
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