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https://issues.apache.org/jira/browse/HBASE-13376?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14549682#comment-14549682
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Ted Yu commented on HBASE-13376:
--------------------------------
The test failure can be reproduced:
{code}
testRebalanceOnRegionServerNumberChange[1](org.apache.hadoop.hbase.TestRegionRebalancing)
Time elapsed: 8.44 sec <<< ERROR!
java.lang.NullPointerException: null
at
org.apache.hadoop.hbase.master.balancer.BaseLoadBalancer$Cluster$2.compare(BaseLoadBalancer.java:772)
at
org.apache.hadoop.hbase.master.balancer.BaseLoadBalancer$Cluster$2.compare(BaseLoadBalancer.java:769)
at java.util.TimSort.countRunAndMakeAscending(TimSort.java:324)
at java.util.TimSort.sort(TimSort.java:189)
at java.util.TimSort.sort(TimSort.java:173)
at java.util.Arrays.sort(Arrays.java:659)
at
org.apache.hadoop.hbase.master.balancer.BaseLoadBalancer$Cluster.sortServersByLocality(BaseLoadBalancer.java:762)
at
org.apache.hadoop.hbase.master.balancer.BaseLoadBalancer$Cluster.getLowestLocalityRegionServer(BaseLoadBalancer.java:788)
at
org.apache.hadoop.hbase.master.balancer.StochasticLoadBalancer$LocalityBasedCandidateGenerator.pickLowestLocalityServer(StochasticLoadBalancer.java:625)
at
org.apache.hadoop.hbase.master.balancer.StochasticLoadBalancer$LocalityBasedCandidateGenerator.generate(StochasticLoadBalancer.java:597)
at
org.apache.hadoop.hbase.master.balancer.StochasticLoadBalancer.balanceCluster(StochasticLoadBalancer.java:266)
at org.apache.hadoop.hbase.master.HMaster.balance(HMaster.java:1241)
at
org.apache.hadoop.hbase.TestRegionRebalancing.testRebalanceOnRegionServerNumberChange(TestRegionRebalancing.java:119)
{code}
The NPE seems to come from this line in BaseLoadBalancer$Cluster$2.compare :
{code}
float locality1 = getLocality(integer);
{code}
> Improvements to Stochastic load balancer
> ----------------------------------------
>
> Key: HBASE-13376
> URL: https://issues.apache.org/jira/browse/HBASE-13376
> Project: HBase
> Issue Type: Improvement
> Components: Balancer
> Affects Versions: 1.0.0, 0.98.12
> Reporter: Vandana Ayyalasomayajula
> Assignee: Vandana Ayyalasomayajula
> Priority: Minor
> Attachments: HBASE-13376_0.98.txt, HBASE-13376_0.txt,
> HBASE-13376_98.patch
>
>
> There are two things this jira tries to address:
> 1. The locality picker in the stochastic balancer does not pick regions with
> least locality as candidates for swap/move. So when any user configures
> locality cost in the configs, the balancer does not always seems to move
> regions with bad locality.
> 2. When a cluster has equal number of loaded regions, it always picks the
> first one. It should pick a random region on one of the equally loaded
> servers. This improves a chance of finding a good candidate, when load picker
> is invoked several times.
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