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From "Ted Yu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-7060) region load balancing by table does not handle the case where a table's region count is less than the number of the RS in the cluter
Date Mon, 29 Oct 2012 19:26:12 GMT

    [ https://issues.apache.org/jira/browse/HBASE-7060?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13486267#comment-13486267
] 

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

Nice finding.
{code}
+      if (regionToTake == 0)
+      {
+        regionToTake = 1;
{code}
The above would produce unnecessarily high number of underloaded servers, right ?
                
> region load balancing by table does not handle the case where a table's region count
is less than the number of the RS in the cluter
> ------------------------------------------------------------------------------------------------------------------------------------
>
>                 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: Tianying Chang
>         Attachments: 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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