[HBASE-6760] HMaster.balance() returns 'true' even if rebalancing plan is empty and the balancer does not run

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Invalid
• Component/s: master
• Assignee: Unassigned
• Reporter: Aditya Kishore
• Created: 11/Sep/12 18:33
• Updated: 14/Jun/22 17:56
• Resolved: 08/Jan/15 08:07

Description

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.

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()) {
....

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.