[HBASE-12762] Region with no hfiles will have the highest locality cost in LocalityCostFunction

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 0.99.2
• Fix Version/s: 1.0.0, 0.98.10, 1.1.0
• Component/s: Balancer
• Hadoop Flags: Reviewed
• Assignee: Jianwei Cui
• Reporter: Jianwei Cui
• Created: 27/Dec/14 12:33
• Updated: 06/Apr/18 17:54
• Resolved: 30/Dec/14 18:10

Description

The locality cost of region will be computed in LocalityCostFunction.cost as:

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;
        }
        ...
    }

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:

   ...
        if (index < 0) {
          if (regionLocation.length > 0) { //  ==> only consider regions with hfiles
              cost += 1;
          }
        } else {
          cost += (double) index / (double) regionLocations.length;
        }
   ...