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https://issues.apache.org/jira/browse/HBASE-17110?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15710807#comment-15710807
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Yu Li commented on HBASE-17110:
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Pushed into master branch, could not directly apply to branch-1 so will wait
for the branch-1 patch before closing this JIRA.
Thanks all for review.
> Improve SimpleLoadBalancer to always take server-level balance into account
> ---------------------------------------------------------------------------
>
> Key: HBASE-17110
> URL: https://issues.apache.org/jira/browse/HBASE-17110
> Project: HBase
> Issue Type: Improvement
> Components: Balancer
> Affects Versions: 2.0.0, 1.2.4
> Reporter: Charlie Qiangeng Xu
> Assignee: Charlie Qiangeng Xu
> Fix For: 2.0.0
>
> Attachments: HBASE-17110-V2.patch, HBASE-17110-V3.patch,
> HBASE-17110-V4.patch, HBASE-17110-V5.patch, HBASE-17110-V6.patch,
> HBASE-17110-V7.patch, HBASE-17110-V8.patch, HBASE-17110.patch
>
>
> Currently with bytable strategy there might still be server-level imbalance
> and we will improve this in this JIRA.
> Some more background:
> When operating large scale clusters(our case), some companies still prefer to
> use {{SimpleLoadBalancer}} due to its simplicity, quick balance plan
> generation, etc. Current SimpleLoadBalancer has two modes:
> 1. byTable, which only guarantees that the regions of one table could be
> uniformly distributed.
> 2. byCluster, which ignores the distribution within tables and balance the
> regions all together.
> If the pressures on different tables are different, the first byTable option
> is the preferable one in most case. Yet, this choice sacrifice the cluster
> level balance and would cause some servers to have significantly higher load,
> e.g. 242 regions on server A but 417 regions on server B.(real world stats)
> Consider this case, a cluster has 3 tables and 4 servers:
> {noformat}
> server A has 3 regions: table1:1, table2:1, table3:1
> server B has 3 regions: table1:2, table2:2, table3:2
> server C has 3 regions: table1:3, table2:3, table3:3
> server D has 0 regions.
> {noformat}
> From the byTable strategy's perspective, the cluster has already been
> perfectly balanced on table level. But a perfect status should be like:
> {noformat}
> server A has 2 regions: table2:1, table3:1
> server B has 2 regions: table1:2, table3:2
> server C has 3 regions: table1:3, table2:3, table3:3
> server D has 2 regions: table1:1, table2:2
> {noformat}
> We can see the server loads change from 3,3,3,0 to 2,2,3,2, while the table1,
> table2 and table3 still keep balanced. And this is the goal this JIRA tries
> to achieve.
> Two UTs will be added as well with the last one demonstrating advantage of
> the new strategy. Also, a onConfigurationChange method will be implemented to
> hot control the "slop" variable.
> We have been using the strategy on our largest cluster for several months, so
> the effect could be assured to some extent.
>
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