ASF GitHub Bot commented on HELIX-674:

Github user mcvsubbu commented on a diff in the pull request:

    --- Diff: 
    @@ -0,0 +1,94 @@
    +package org.apache.helix.controller.rebalancer.constraint;
    + * Licensed to the Apache Software Foundation (ASF) under one
    + * or more contributor license agreements.  See the NOTICE file
    + * distributed with this work for additional information
    + * regarding copyright ownership.  The ASF licenses this file
    + * to you under the Apache License, Version 2.0 (the
    + * "License"); you may not use this file except in compliance
    + * with the License.  You may obtain a copy of the License at
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    + *   http://www.apache.org/licenses/LICENSE-2.0
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    +import org.apache.helix.controller.common.ResourcesStateMap;
    +import org.apache.helix.controller.rebalancer.util.ResourceUsageCalculator;
    +import java.util.HashMap;
    +import java.util.Map;
    +public class PartitionWeightAwareEvennessConstraint extends 
AbstractRebalanceSoftConstraint {
    +  private final int _weight;
    +  private final PartitionQuotaProvider _partitionQuotaProvider;
    +  private final CapacityProvider _capacityProvider;
    +  // Use to track any assignments that are proposed during the rebalance 
    +  // Note these assignments are not reflected in providers.
    +  private final Map<String, Integer> _pendingUsage;
    +  public PartitionWeightAwareEvennessConstraint(PartitionQuotaProvider 
    +      CapacityProvider capacityProvider, int weight) {
    +    _partitionQuotaProvider = partitionQuotaProvider;
    +    _capacityProvider = capacityProvider;
    +    _weight = weight;
    --- End diff --
    Not clear what this weight means. Does this mean the relative importance of 
this constraint vs any other? If so, maybe we should consider naming these 
correctly. we have partition weights and constraint weights....
    Also, _weight is not used in the class?  Should it move to the super class?

> Constraint Based Resource Rebalancer
> ------------------------------------
>                 Key: HELIX-674
>                 URL: https://issues.apache.org/jira/browse/HELIX-674
>             Project: Apache Helix
>          Issue Type: New Feature
>            Reporter: Jiajun Wang
>            Assignee: Jiajun Wang
>            Priority: Major
>             Fix For: 0.8.x
>         Attachments: Constraint-BasedResourceRebalancing-080318-2226-240.pdf
> Helix rebalancer assigns resources according to different strategies. 
> Recently, we optimize the strategy for evenness and minimize movement. 
> However, the evenness here only applies to partition numbers. Moreover, we've 
> got more requests for customizable rebalancer from our users.
> Take partition weight as an example:
> In reality, partition replicas have different size. We use "partition weight" 
> as an abstraction of the partition size. It can be network traffic usage, 
> disk usage, or any other combined factors.
> Given each partition may have different weights, Helix should be able to 
> assign partition accordingly. So that the distribution would be even 
> regarding the weight.
> In this project, we are planning new rebalancer mechanism that generates 
> resource partition assignment according to a list of "constraints". Current 
> rebalance strategy can be regarded as one kind of constraint. Moving forward, 
> Helix users would be able to extend the constraint interface using their own 
> logic.
> Some init discussions are in progress and we will have a proposal posted here 
> soon.

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