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From "Jean-Daniel Cryans (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-9601) Use a faster balancer when the imbalance is in the hundreds of regions
Date Fri, 20 Sep 2013 21:00:55 GMT
Jean-Daniel Cryans created HBASE-9601:
-----------------------------------------

             Summary: Use a faster balancer when the imbalance is in the hundreds of regions
                 Key: HBASE-9601
                 URL: https://issues.apache.org/jira/browse/HBASE-9601
             Project: HBase
          Issue Type: Improvement
    Affects Versions: 0.96.0
            Reporter: Jean-Daniel Cryans
             Fix For: 0.98.0, 0.96.1


Something I'm noticing is that the new balancer is good at optimizing the balance when it
needs to move a handful of regions, but once the imbalance is in the hundreds then it might
be better if we used something speedier.

For example, I have a small 5 nodes cluster that I use to test with a lot of regions, 10k
to be precise. The average load should be 2000, but killing one RS will make the average go
to 2500, and when the RS comes back there's 2000 regions to move. When I call the balancer
it spends 30 seconds to be able to move 150-300 regions, so in order to go back to a good
balancer cluster-wide it takes me a few runs, but if the balancer was doing it by itself (with
the 5 minutes wait), it could take hours. Maybe not a bad thing in prod although getting your
locality back might be a good idea as well as offloading the machines.

So it seems that we need to be able to detect this situation and only balance based on load
average, and maybe locality (so that the original regions would move back, hopefully).

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