huaxiangsun commented on a change in pull request #3724:
URL: https://github.com/apache/hbase/pull/3724#discussion_r736784079
##########
File path:
hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/balancer/DoubleArrayCost.java
##########
@@ -66,17 +66,21 @@ void applyCostsChange(Consumer<double[]> consumer) {
}
private static double computeCost(double[] stats) {
+ if (stats == null || stats.length == 0) {
+ return 0;
+ }
double totalCost = 0;
double total = getSum(stats);
double count = stats.length;
double mean = total / count;
-
for (int i = 0; i < stats.length; i++) {
double n = stats[i];
double diff = (mean - n) * (mean - n);
totalCost += diff;
}
+ // No need to compute standard deviation with division by cluster size
when scaling.
+ totalCost = Math.sqrt(totalCost);
Review comment:
A bit confused. totalCost is the sum of standard deviation. What is
square root of this sum?
If there is no need to compute standard deviation, should the standard
deviation be avoided at the first place?
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