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https://issues.apache.org/jira/browse/HBASE-6760?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13453321#comment-13453321
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Aditya Kishore commented on HBASE-6760:
---------------------------------------
The balancer truly runs only if the re-balancing plan is calculated as not null
AND not empty. i.e. within the condition
{code}
if (plans != null && !plans.isEmpty()) {
//run balancer
}
{code}
Further the contract of HMaster.balance() is to return true iff the balancer
actually runs and re-balances the region assignments. So the name blancerRan,
which is also stores the return value of the function, seems appropriate.
Further, IMO, "this.cpHost.postBalance();" should only be called if the
balancer has run. Or at the least pass this information (true/false or number
of regions balanced in this run) to the CP but that will require interface
change in MasterCoprocessorHost.
> HMaster.balance() returns 'true' even if rebalancing plan is empty and the
> balancer does not run
> ------------------------------------------------------------------------------------------------
>
> Key: HBASE-6760
> URL: https://issues.apache.org/jira/browse/HBASE-6760
> Project: HBase
> Issue Type: Bug
> Components: master
> Reporter: Aditya Kishore
> Assignee: Aditya Kishore
> Priority: Minor
>
> The issue seems to exists due to oversight during the rewrite. In line 1289,
> the variable 'plans' is created as a 'new ArrayList<RegionPlan>()' and then
> in line 1298, balancerRan is calculated as (plans != null) which for obvious
> reason, will always return true.
> {code:title=HMaster.java (trunk:1383496)}
> ....
> 1289 List<RegionPlan> plans = new ArrayList<RegionPlan>();
> 1290 //Give the balancer the current cluster state.
> 1291 this.balancer.setClusterStatus(getClusterStatus());
> 1292 for (Map<ServerName, List<HRegionInfo>> assignments :
> assignmentsByTable.values()) {
> 1293 List<RegionPlan> partialPlans =
> this.balancer.balanceCluster(assignments);
> 1294 if (partialPlans != null) plans.addAll(partialPlans);
> 1295 }
> 1296 int rpCount = 0; // number of RegionPlans balanced so far
> 1297 long totalRegPlanExecTime = 0;
> 1298 balancerRan = plans != null;
> 1299 if (plans != null && !plans.isEmpty()) {
> ....
> {code}
> A simple fix is to initialize 'balancerRan' to 'false', remove "balancerRan =
> plans != null" and add "balancerRan = true" after "if (plans != null &&
> !plans.isEmpty()) {".
> However, a question remains that should we call "this.cpHost.postBalance();"
> if the balancer did not run at this point?
> I'll attach the patch shortly if I get a confirmation on this.
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