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https://issues.apache.org/jira/browse/HDFS-16949?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17706541#comment-17706541
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ASF GitHub Bot commented on HDFS-16949:
---------------------------------------
rdingankar commented on code in PR #5495:
URL: https://github.com/apache/hadoop/pull/5495#discussion_r1152330757
##########
hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/metrics2/util/TestSampleQuantiles.java:
##########
@@ -118,4 +119,40 @@ public void testQuantileError() throws IOException {
}
}
}
+
+ /**
+ * Correctness test that checks that absolute error of the estimate for
inverse quantiles
+ * is within specified error bounds for some randomly permuted streams of
items.
+ */
+ @Test
+ public void testInverseQuantiles() throws IOException {
+ SampleQuantiles inverseQuantilesEstimator = new
SampleQuantiles(MutableInverseQuantiles.INVERSE_QUANTILES);
+ final int count = 100000;
+ Random r = new Random(0xDEADDEAD);
Review Comment:
The Random object is used as source of randomness to shuffle the sample
array.
> Update ReadTransferRate to ReadLatencyPerGB for effective percentile metrics
> ----------------------------------------------------------------------------
>
> Key: HDFS-16949
> URL: https://issues.apache.org/jira/browse/HDFS-16949
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Reporter: Ravindra Dingankar
> Assignee: Ravindra Dingankar
> Priority: Minor
> Labels: pull-request-available
> Fix For: 3.3.0, 3.4.0
>
>
> HDFS-16917 added ReadTransferRate quantiles to calculate the rate which data
> is read per unit of time.
> With percentiles the values are sorted in ascending order and hence for the
> transfer rate p90 gives us the value where 90 percent rates are lower
> (worse), p99 gives us the value where 99 percent values are lower (worse).
> Note that value(p90) < p(99) thus p99 is a better transfer rate as compared
> to p90.
> However as the percentile increases the value should become worse in order to
> know how good our system is.
> Hence instead of calculating the data read transfer rate, we should calculate
> it's inverse. We will instead calculate the time taken for a GB of data to be
> read. ( seconds / GB )
> After this the p90 value will give us 90 percentage of total values where the
> time taken is less than value(p90), similarly for p99 and others.
> Also p(90) < p(99) and here p(99) will become a worse value (taking more time
> each byte) as compared to p(90)
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