clarax commented on a change in pull request #3724:
URL: https://github.com/apache/hbase/pull/3724#discussion_r736888044
##########
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:
Total cost = sqrt(sum(square of the deviation)). Since we scale total
cost on min cost and max cost, linearly, I skipped the step to divided all
three of total cost, min cost and max cost by sqrt(count).
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