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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-18946) Stochastic load balancer assigns replica regions to the same RS
Date Mon, 04 Dec 2017 17:19:00 GMT

    [ https://issues.apache.org/jira/browse/HBASE-18946?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16277107#comment-16277107
] 

stack commented on HBASE-18946:
-------------------------------

So, looking at v8 again in light of your comment, won't we end up putting region replicas
on the same servers each time we assign?

The patch is still an advance because you've moved the problem of assign to AM which is where
it belongs; that the implementation has problems is something we can work on ...

bq. I said this because now we set the target server so the round robin logic is not with
the AM. Generally AM decides if the assignment shouldbe round robin or retain assignment.
So here it is always retain assignment. 

Say some more on this please.

Is this right?

110	          if (tableDescriptor.getRegionReplication() > 1) {
111	            addChildProcedure(
112	              env.getAssignmentManager().createRoundRobinAssignProcedures(newRegions));
113	          } else {
114	            addChildProcedure(env.getAssignmentManager().createAssignProcedures(newRegions));
115	          }

Should it be other way around?

I still think this patch really nice.

> Stochastic load balancer assigns replica regions to the same RS
> ---------------------------------------------------------------
>
>                 Key: HBASE-18946
>                 URL: https://issues.apache.org/jira/browse/HBASE-18946
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 2.0.0-alpha-3
>            Reporter: ramkrishna.s.vasudevan
>            Assignee: ramkrishna.s.vasudevan
>             Fix For: 2.0.0-beta-1
>
>         Attachments: HBASE-18946.patch, HBASE-18946.patch, HBASE-18946_2.patch, HBASE-18946_2.patch,
HBASE-18946_simple_7.patch, HBASE-18946_simple_8.patch, TestRegionReplicasWithRestartScenarios.java
>
>
> Trying out region replica and its assignment I can see that some times the default LB
Stocahstic load balancer assigns replica regions to the same RS. This happens when we have
3 RS checked in and we have a table with 3 replicas. When a RS goes down then the replicas
being assigned to same RS is acceptable but the case when we have enough RS to assign this
behaviour is undesirable and does not solve the purpose of replicas. 
> [~huaxiang] and [~enis]. 



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