[jira] [Created] (HBASE-10528) DefaultBalancer selects plans to move regions onto draining nodes

["churro morales (JIRA)" <ji...@apache.org>]

churro morales created HBASE-10528:
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             Summary: DefaultBalancer selects plans to move regions onto draining nodes
                 Key: HBASE-10528
                 URL: https://issues.apache.org/jira/browse/HBASE-10528
             Project: HBase
          Issue Type: Bug
    Affects Versions: 0.94.5
            Reporter: churro morales


We have quite a large cluster > 100k regions, and we needed to isolate a region was very hot until we could push a patch.  We put this region on its own regionserver and set it in the draining state.  The default balancer was selecting regions to move to this cluster for its region plans.  

It just so happened that there were very small regions on the draining servers, which constantly triggered balancing.  Thus we were closing regions, then attempting to move to the draining server finding out its draining.

There are some approaches we can take here.

1. Exclude draining servers altogether, don't even pass those into the load balancer from HMaster.

2. We could exclude draining servers from ceiling and floor calculations where we could potentially skip load balancing because those draining servers wont be represented when deciding whether to balance.

3. Along with #2 when assigning regions, we would skip plans to assign regions to those draining servers.

I am in favor of #1 which is simply removes servers as candidates for balancing if they are in the draining state.

But I would love to hear what everyone else thinks.



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