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From Rajkumar Rajaratnam <rajkum...@wso2.com>
Subject Re: Bug in round-robin partition selection algorithm
Date Tue, 03 Mar 2015 17:27:31 GMT
Hi Lahiru,

Actually, current logic is not working as your example. This logic only
uses the first partition. This will never use any other partitions. See my
comments within the following code.

    public PartitionContext
getNextScaleUpPartitionContext(PartitionContext[] partitionContexts) {

        int selectedIndex = 0;
        int lowestInstanceCount = 0;

        for(int partitionIndex = 0; partitionIndex <
partitionContexts.length - 1; partitionIndex++) {


if(partitionContexts[partitionIndex].getNonTerminatedMemberCount() <
lowestInstanceCount) {

*//  this if condition is always false, because non terminated count is
always >=0*

                lowestInstanceCount =
partitionContexts[partitionIndex].getNonTerminatedMemberCount();
                selectedIndex = partitionIndex;
            }
        }

*//  selected index is 0 always, so round-robin will always use first
partition*
        if(partitionContexts[selectedIndex].getNonTerminatedMemberCount() <
partitionContexts[selectedIndex].getMax()) {

            if(log.isDebugEnabled()){
                log.debug(String.format("[round-robin algorithm] [scale-up]
[partition] %s has space to create members. " +
                        "[non terminated count] %s [max] %s"
                        , partitionContexts[selectedIndex].getPartitionId(),

partitionContexts[selectedIndex].getNonTerminatedMemberCount(),
                        partitionContexts[selectedIndex].getMax()));
            }
            return partitionContexts[selectedIndex];
        } else {

            return null;
        }
    }

May be I am missing something here.

Thanks.

On Tue, Mar 3, 2015 at 10:42 PM, Lahiru Sandaruwan <lahirus@wso2.com> wrote:

> Hi Raj,
>
> Earlier in 4.0.0 release, we have been using the partition index. If that
> to be worked correctly we should persist the index for each cluster.
>
> IMO there is a better way to execute the round-robin method as follows,
>
> The intention of round robin algorithm is to distribute the members in the
> partitions equally. Current method works as per the following example.
>
> Say we have 3 partitions, p1, p2, and p3 and max of each partition is 2.
>
> So according to the algorithm, it will select the first partition who has
> the lowest member count.
>
> Iteration1: It will select p1.
> Iteration2: It will select p2.
> Iteration3: It will select p3.
> Iteration4: It will select p1.
> Iteration5: It will select p2.
> ....
>
> Thanks.
>
>
>
> On Tue, Mar 3, 2015 at 10:22 PM, Rajkumar Rajaratnam <rajkumarr@wso2.com>
> wrote:
>
>> Hi Devs,
>>
>> It seems to me that there is a bug in round-robin implementation of
>> partition algorithm.
>>
>>
>> https://github.com/apache/stratos/blob/0b7734f4c9f1444d064fec93bf9ac59a5883faf2/components/org.apache.stratos.autoscaler/src/main/java/org/apache/stratos/autoscaler/algorithm/RoundRobin.java#L43-L64
>>
>> Shouldn't it work based on current partition index? For example, if the
>> most recent instance was spin up in partition-1, the next instance should
>> be spin up in partition-2 and so on. According to current logic what is
>> happening is, all the instance are spin up in partition-1.
>>
>> Please correct me If I am wrong.
>>
>> Thanks.
>>
>> --
>> Rajkumar Rajaratnam
>> Committer & PMC Member, Apache Stratos
>> Software Engineer, WSO2
>>
>> Mobile : +94777568639
>> Blog : rajkumarr.com
>>
>
>
>
> --
> --
> Lahiru Sandaruwan
> Committer and PMC member, Apache Stratos,
> Senior Software Engineer,
> WSO2 Inc., http://wso2.com
> lean.enterprise.middleware
>
> email: lahirus@wso2.com blog: http://lahiruwrites.blogspot.com/
> linked-in: http://lk.linkedin.com/pub/lahiru-sandaruwan/16/153/146
>
>


-- 
Rajkumar Rajaratnam
Committer & PMC Member, Apache Stratos
Software Engineer, WSO2

Mobile : +94777568639
Blog : rajkumarr.com

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