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https://issues.apache.org/jira/browse/HBASE-17110?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15670116#comment-15670116
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Anoop Sam John commented on HBASE-17110:
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Interesting.. Why you think this can not be an improvement for the byTable
strategy but a new strategy?
I see not a new strategy but a config based extension of byTable strategy.
But my doubt is why such a config needed? Why can't the SimpleLB byTable
strategy do this always? First preference to balance by table and then make
sure the overall balance also achieved. I mean at balance time, even if it sees
by tables it is perfect, don't stop there and try find a more perfect cluster
level balance. Than a new config requirement, we can do it always. I can see
the new config is default OFF. May be on existing patch branches u dont want a
behave change? At least for master, I feel at least the config to be ON by
default.. And IMO the config itself not required. Why we should not allow this
better balancing to work?
> 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 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 what the new mode "byTableOverall" can achieve.
> Two UTs have been added as well and the last one demonstrates the advantage
> of the new strategy.
> Also, a onConfigurationChange method has been implemented to hot control the
> "slop" variable.
>
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