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From "cuijianwei (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-12762) Region with no hfiles will have the highest locality cost in LocalityCostFunction
Date Sat, 27 Dec 2014 12:34:13 GMT
cuijianwei created HBASE-12762:
----------------------------------

             Summary: Region with no hfiles will have the highest locality cost in LocalityCostFunction
                 Key: HBASE-12762
                 URL: https://issues.apache.org/jira/browse/HBASE-12762
             Project: HBase
          Issue Type: Improvement
          Components: Balancer
    Affects Versions: 0.99.2
            Reporter: cuijianwei
            Priority: Minor


The locality cost of region will be computed in LocalityCostFunction.cost as:
{code}
double cost() {
        ...
        int index = -1;
        for (int j = 0; j < regionLocations.length; j++) {
          if (regionLocations[j] >= 0 && regionLocations[j] == serverIndex) {
            index = j;
            break;
          }
        }

        if (index < 0) {
          cost += 1;  // ==> region with no hfiles will have the highest cost
        } else {
          cost += (double) index / (double) regionLocations.length;
        }
        ...
    }
{code}
The region with no hfiles(such as empty region) will have the highest cost which represents
the worst case that region located in the server with no locality for hfiles. However, this
might be the best case because there are no hlogs for the region. Although the absolute cost
value won't affect the balance process, will it be more reasonable to have zero cost for such
regions, such as:
{code}
   ...
        if (index < 0) {
          if (regionLocation.length > 0) { //  ==> only consider regions with hfiles
              cost += 1;
          }
        } else {
          cost += (double) index / (double) regionLocations.length;
        }
   ...
{code} 



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