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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