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From "Charlie Qiangeng Xu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-17110) Add an "Overall Strategy" option(balanced both on table level and server level) to SimpleLoadBalancer
Date Thu, 17 Nov 2016 04:05:58 GMT

    [ https://issues.apache.org/jira/browse/HBASE-17110?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15672653#comment-15672653

Charlie Qiangeng Xu commented on HBASE-17110:

Thank you for looking into the code [~tedyu] and [~anoop.hbase], I've changed the strategy
to be default.
And also follow [~tedyu]'s suggestion I change the format and replace the variable initialnumRegions
wherever possible.
After a second thought, I think using standard deviation might be some how redundant.
I've already used "slop" to set the threshold, thus another criterion would over-complicate
the control(hard for user, also have to introduce another conf setting if not be hardcoded
to 10). So I remove it as well.
A new patch HBASE-17110-V2.patch has been uploaded :)

> Add an "Overall Strategy" option(balanced both on table level and server level) to SimpleLoadBalancer
> -----------------------------------------------------------------------------------------------------
>                 Key: HBASE-17110
>                 URL: https://issues.apache.org/jira/browse/HBASE-17110
>             Project: HBase
>          Issue Type: New Feature
>          Components: Balancer
>    Affects Versions: 2.0.0, 1.2.4
>            Reporter: Charlie Qiangeng Xu
>            Assignee: Charlie Qiangeng Xu
>         Attachments: HBASE-17110.patch, SimpleBalancerBytableOverall.V1
> This jira is about an enhancement of simpleLoadBalancer. Here we introduce a new strategy:
"bytableOverall" which could be controlled by adding:
> {noformat}
> <property>
>   <name>hbase.master.loadbalance.bytableOverall</name>
>   <value>true</value>
> </property>
> {noformat}
> We have been using the strategy on our largest cluster for several months. it's proven
to be very helpful and stable, especially, the result is quite visible to the users.
> Here is the reason why it's helpful:
> 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
> 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 what the new mode "byTableOverall" can achieve.
> Two UTs have been added as well and the last one demonstrates the advantage of the new
> Also, a onConfigurationChange method has been implemented to hot control the "slop" variable.

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