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From: "Ted Yu (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (HBASE-7060) Region load balancing by table does
 not handle the case where a table's region count is lower than the number
 of the RS in the cluster
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    [ https://issues.apache.org/jira/browse/HBASE-7060?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13486663#comment-13486663 ] 

Ted Yu commented on HBASE-7060:
-------------------------------

Here is result for 0.92 test suite:
{code}
Failed tests:   queueFailover(org.apache.hadoop.hbase.replication.TestReplication): Waited too much time for queueFailover replication. Waited 44939ms.

Tests run: 1161, Failures: 1, Errors: 0, Skipped: 8

[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2:00:37.302s
{code}
The test failure was not related to the patch.
                
> Region load balancing by table does not handle the case where a table's region count is lower than the number of the RS in the cluster
> --------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HBASE-7060
>                 URL: https://issues.apache.org/jira/browse/HBASE-7060
>             Project: HBase
>          Issue Type: Bug
>          Components: master
>    Affects Versions: 0.92.0
>            Reporter: Tianying Chang
>            Assignee: Ted Yu
>             Fix For: 0.92.3, 0.94.3
>
>         Attachments: 7060-94.txt, HBASE-7060.patch
>
>
> When the table's region count is less than the count of region servers, the region balance algorithm will not move the region. For example, the cluster has 100 RS, the table has 50 regions sitting on one RS, they will not be moved to any of the other 99 RS.
> This is because the algorithm did not calculate the under-loaded RS correctly. This is how the algorithm works with the above example:
> avg-regions-per-RS=0.5
> min-RS-per-RS=0
> max-RS-per-RS=1
> when they calculate the under loaded RS, the code is as below. Since regionCount=0, which is always >=min, so it will always skip, therefore, no underloaded RS are found.
> Map<ServerName, Integer> underloadedServers = new HashMap<ServerName, Integer>();
> for (Map.Entry<ServerAndLoad, List<HRegionInfo>> server:
> serversByLoad.entrySet()) {
> int regionCount = server.getKey().getLoad();
> if (regionCount >= min) { break; }
> underloadedServers.put(server.getKey().getServerName(), min - regionCount);
> }
> Later the function returns since underloaded RS size is 0
> if (serverUnerloaded ==0) return regionsToReturn;

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