ASF GitHub Bot commented on HELIX-674:

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

    --- Diff: 
helix-core/src/main/java/org/apache/helix/util/WeightAwareRebalanceUtil.java ---
    @@ -0,0 +1,141 @@
    +package org.apache.helix.util;
    +import org.apache.helix.HelixException;
    +import org.apache.helix.ZNRecord;
    +import org.apache.helix.api.config.RebalanceConfig;
    +import org.apache.helix.controller.common.PartitionStateMap;
    +import org.apache.helix.controller.common.ResourcesStateMap;
    +import org.apache.helix.controller.stages.ClusterDataCache;
    +import org.apache.helix.model.*;
    +import java.util.ArrayList;
    +import java.util.HashMap;
    +import java.util.List;
    +import java.util.Map;
    + * A rebalance tool that generate an resource partition assignment based 
on the input.
    + * Note the assignment won't be automatically applied to the cluster. 
Applications are supposed to
    + * apply the change.
    + */
    --- End diff --
    Good to have extensive javadoc on how to use this tool. Perhaps you  intend 
users to see the tests, in which case you can point to a test on how to use it. 
One example with zk and one without will be ideal. Thanks.

> 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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