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https://issues.apache.org/jira/browse/HBASE-25726?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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David Manning updated HBASE-25726:
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Status: Patch Available (was: Open)
> MoveCostFunction is not included in the list of cost functions for
> StochasticLoadBalancer
> -----------------------------------------------------------------------------------------
>
> Key: HBASE-25726
> URL: https://issues.apache.org/jira/browse/HBASE-25726
> Project: HBase
> Issue Type: Bug
> Components: Balancer
> Affects Versions: 2.4.0, 2.3.1, 3.0.0-alpha-1, 1.7.0
> Reporter: David Manning
> Assignee: David Manning
> Priority: Major
>
> After OffPeakHours fix for MoveCostFunction (HBASE-24709), MoveCostFunction
> is no longer included in costFunctions list. {{addCostFunction}} expects
> multiplier to be non-zero, but multiplier is now only set in {{cost}}
> function.
> As a result, {{hbase.master.balancer.stochastic.maxMovePercent}} is not
> respected, and there is no cost function to oppose a move. Any move that
> decreases total cost at all will be accepted, causing more churn and
> disruption from balancer executions.
> We noticed this when investigating a case where the balancer would run after
> a regionserver was restarted without use of region_mover script. The
> regionserver comes online with 0 regions, leading to a shortcut in
> {{needsBalance}} for {{idleRegionServerExist}}. The balancer runs to move
> regions to that newly restarted regionserver. However, it moves a large
> number of regions in the cluster, hyper-optimizing the other cost variables.
> There were ~4300 regions in the cluster at the time, so moving 25% of the
> regions should have had a final cost of at least 7 (default moveCostFunction
> weight.) MoveCostFunction is also not listed in the functions contributing to
> the initial cost.
> {{2021-03-30 15:47:43,396 INFO [49187_ChoreService_3]
> balancer.StochasticLoadBalancer - start StochasticLoadBalancer.balancer,
> initCost=12.91377229840024, functionCost=RegionCountSkewCostFunction :
> (500.0, 0.014878672009326464); TableSkewCostFunction : (35.0,
> 0.013600280177445717); RegionReplicaHostCostFunction : (100000.0, 0.0);
> RegionReplicaRackCostFunction : (10000.0, 0.0); ReadRequestCostFunction :
> (5.0, 0.8296332203204705); WriteRequestCostFunction : (5.0,
> 0.06818455421617946); MemstoreSizeCostFunction : (5.0, 0.08132131691669181);
> StoreFileCostFunction : (5.0, 0.02054620605193966); computedMaxSteps:
> 1000000}}
> {{2021-03-30 15:48:13,385 DEBUG [49187_ChoreService_3]
> balancer.StochasticLoadBalancer - Finished computing new load balance plan.
> Computation took 30004ms to try 6571 different iterations. Found a solution
> that moves 1095 regions; Going from a computed cost of 12.91377229840024 to a
> new cost of 4.804625730746651}}
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