[GitHub] [ozone] JacksonYao287 commented on pull request #2756: HDDS-5602. always choose the nearest one as the target in the candidates according to networkTopology

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JacksonYao287 commented on pull request #2756:
URL: https://github.com/apache/ozone/pull/2756#issuecomment-983448371


   thanks @lokeshj1703 very much for the review!
   >I think it is better to have a separated ContainerBalancerSelectionCriteria as it gives flexibility later to account both source and target limitations in the criteria.
   for now , the only role of ContainerBalancerSelectionCriteria is to get Candidate Containers. but i agree with you. may be later in the future, we need to do some flexible work in ContainerBalancerSelectionCriteria. so let us keep it for now and i will cancel this refactor.
   
   so in this patch , i will only do the network topology related work. so i want to hear your opinion, should we sorting candidate targets by network first, or make it configurable? 
   if we sort candidate targets by network first, we will then use a common list instead of current Treeset to hold all the candidate targets, and we should sort all the candidate targets for each source datanode with a function , for example:
   ```
   List<DatanodeUsageInfo> potentialTargets;
   DatanodeUsageInfo source;
   NetworkTopology nt = scm.getClusterMap();
   //for each source, we should sort
   potentialTargets.sort((a, b) -> {
       // sort by network topology first
        int ret = 0;
        int distancetoA = nt.getDistanceCost(source, a);
        int distancetoB =  nt.getDistanceCost(source, b);
        ret = distancetoA - distancetoB;
        if (ret != 0) {
                return ret;
        }
       // if network distance is equal, sort by usage
         double currentUsageOfA = a.calculateUtilization(
             sizeEnteringNode.get(a.getDatanodeDetails()));
         double currentUsageOfB = b.calculateUtilization(
             sizeEnteringNode.get(b.getDatanodeDetails()));
         ret = Double.compare(currentUsageOfA, currentUsageOfB);
         if (ret != 0) {
           return ret;
         }
         UUID uuidA = a.getDatanodeDetails().getUuid();
         UUID uuidB = b.getDatanodeDetails().getUuid();
         return uuidA.compareTo(uuidB);
       })
   ```
   
   


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