Jean-Daniel Cryans created HBASE-9601:
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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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