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From "Charlie Qiangeng Xu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-17039) SimpleLoadBalancer schedules large amount of invalid region moves
Date Mon, 07 Nov 2016 17:18:58 GMT

    [ https://issues.apache.org/jira/browse/HBASE-17039?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15644764#comment-15644764
] 

Charlie Qiangeng Xu commented on HBASE-17039:
---------------------------------------------

Just skimmed through the historical changes for this part,  
I found the code causing problem right now could be attributed to HBASE-7060.
The problem mentioned in that Jira has been handled nicely by other part of current balancer
logic,
yet the code block aforementioned would only cause problem right now.
[~yuzhihong@gmail.com], it seems you were involved in that JIRA, any interest to take a look
at this one?

> SimpleLoadBalancer schedules large amount of invalid region moves
> -----------------------------------------------------------------
>
>                 Key: HBASE-17039
>                 URL: https://issues.apache.org/jira/browse/HBASE-17039
>             Project: HBase
>          Issue Type: Bug
>          Components: Balancer
>    Affects Versions: 2.0.0, 1.2.3, 1.1.7
>            Reporter: Charlie Qiangeng Xu
>            Assignee: Charlie Qiangeng Xu
>         Attachments: HBASE-17039.patch
>
>
> After increasing one of our clusters to 1600 nodes, we observed a large amount of invalid
region moves(more than 30k moves) fired by the balance chore. Thus we simulated the problem
and printed out the balance plan, only to find out many servers that had two regions for a
certain table(we use by table strategy), sent out both regions to other two servers that have
zero region. 
> In the SimpleLoadBalancer's balanceCluster function,
> the code block that determines the underLoadedServers might have a problem:
> {code}
>       if (load >= min && load > 0) {
>         continue; // look for other servers which haven't reached min
>       }
>       int regionsToPut = min - load;
>       if (regionsToPut == 0)
>       {
>         regionsToPut = 1;
>       }
> {code}
> if min is zero, some server that has load of zero, which equals to min would be marked
as underloaded, which would cause the phenomenon mentioned above.
> Since we increased the cluster's size to 1600+, many tables that only have 1000 regions,
now would encounter such issue.
> By fixing it up, the balance plan went back to normal.



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