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https://issues.apache.org/jira/browse/HBASE-25882?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Xiaolin Ha updated HBASE-25882:
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Description:
When using balance by table, the StochasticLoadBalancer will create the cluster
state according to the regions distribution of only one table. As a result,
the TableSkewCostFunction should be replaced by the RegionCountSkewCostFunction
when the table count of the cluster state is less than 2.
The most important problem is that, TableSkewCostFunction will cause
unnecessary calculation steps when there is only one table.
For example，we have 40000+ regions for one table in one group, balance this
table may calculate lots of steps, but we can avoid duplicate computing costs
of TableSkewCostFunction while computing cost of RegionCountSkewCostFunction
and balancing by table.
!image-2021-08-17-20-20-12-768.png|width=907,height=164!
was:
When using balance by table, the StochasticLoadBalancer will create the cluster
state according to the regions distribution of only one table. As a result,
the TableSkewCostFunction should be replaced by the RegionCountSkewCostFunction
when the table count of the cluster state is less than 2.
The most important problem is that, TableSkewCostFunction will cause
unnecessary calculation steps when there is only one table. The cost it
computed may be incorrect.
For example, there are 5 online regionservers, and there is only one table with
exactly one region, the cluster state is [0,0,0,0,1]. Then the cost of
TableSkewCostFunction will be 1 (expect value is 0), because max=1, min=0.25,
value=1. And the computedMaxSteps will be larger than 0, some balance actions
will be generated to decrease the cost. But all the actions is meaningless for
the skew count.
> TableSkewCostFunction may cost unnecessary calculation steps when balancing
> by table
> ------------------------------------------------------------------------------------
>
> Key: HBASE-25882
> URL: https://issues.apache.org/jira/browse/HBASE-25882
> Project: HBase
> Issue Type: Improvement
> Components: Balancer
> Affects Versions: 3.0.0-alpha-1, 2.0.0
> Reporter: Xiaolin Ha
> Assignee: Xiaolin Ha
> Priority: Major
> Attachments: image-2021-08-17-20-20-12-768.png
>
>
> When using balance by table, the StochasticLoadBalancer will create the
> cluster state according to the regions distribution of only one table. As a
> result, the TableSkewCostFunction should be replaced by the
> RegionCountSkewCostFunction when the table count of the cluster state is less
> than 2.
> The most important problem is that, TableSkewCostFunction will cause
> unnecessary calculation steps when there is only one table.
> For example，we have 40000+ regions for one table in one group, balance this
> table may calculate lots of steps, but we can avoid duplicate computing costs
> of TableSkewCostFunction while computing cost of RegionCountSkewCostFunction
> and balancing by table.
>
> !image-2021-08-17-20-20-12-768.png|width=907,height=164!
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