[jira] [Resolved] (HBASE-26872) Load rate calculator for cost functions should be more precise

["Xiaolin Ha (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HBASE-26872?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Xiaolin Ha resolved HBASE-26872.
--------------------------------
    Resolution: Fixed

> Load rate calculator for cost functions should be more precise
> --------------------------------------------------------------
>
>                 Key: HBASE-26872
>                 URL: https://issues.apache.org/jira/browse/HBASE-26872
>             Project: HBase
>          Issue Type: Improvement
>          Components: Balancer
>    Affects Versions: 2.4.11
>            Reporter: Xiaolin Ha
>            Assignee: Xiaolin Ha
>            Priority: Major
>             Fix For: 2.5.0, 3.0.0-alpha-3, 2.4.12
>
>
> The rate calculator should avoid negative values, e.g. if a region is moved from RS1 to RS2, the request count loads in the balancer cache maybe [100,200,0,100,200], then the region load cost calculated by CostFromRegionLoadAsRateFunction#getRegionLoadCost will be (100-200+100+100)/4=25, while the real cost is (100+0+100+200)/4=100. 
> {code:java}
> protected double getRegionLoadCost(Collection<BalancerRegionLoad> regionLoadList) {
>   Iterator<BalancerRegionLoad> iter = regionLoadList.iterator();
>   if (!iter.hasNext()) {
>     return 0;
>   }
>   double previous = getCostFromRl(iter.next());
>   if (!iter.hasNext()) {
>     return 0;
>   }
>   double cost = 0;
>   do {
>     double current = getCostFromRl(iter.next());
>     cost += current - previous;
>     previous = current;
>   } while (iter.hasNext());
>   return Math.max(0, cost / (regionLoadList.size() - 1));
> } {code}
> We should change the cost accumulate codes to,
> {code:java}
> cost += current >= previous ? current - previous : current; {code}



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