[jira] [Created] (HBASE-25697) StochasticBalancer improvement for large scale clusters

["Clara Xiong (Jira)" <ji...@apache.org>]

Clara Xiong created HBASE-25697:
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             Summary: StochasticBalancer improvement for large scale clusters
                 Key: HBASE-25697
                 URL: https://issues.apache.org/jira/browse/HBASE-25697
             Project: HBase
          Issue Type: Improvement
          Components: Balancer, master, UI
            Reporter: Clara Xiong


h2. Findings on a large scale cluster (100,000 regions on 300 nodes)
 * Balancer starts and stops before getting a plan
 * Adding new racks doesn’t trigger balancer
 * Balancer stops leaving some racks at 50% lower region counts
 * Regions for large tables don’t get evenly distributed
 * Observability is poor
 * Too many knobs makes tuning empirical and takes many experiments

h2. Improvements made and bing made
 * Cost function enhancement to capture outliers especially table skew. https://issues.apache.org/jira/browse/HBASE-25625?filter=-2 
 * Explain why balancer stops https://issues.apache.org/jira/browse/HBASE-25666 will back port too https://issues.apache.org/jira/browse/HBASE-24528

h2. More proposals
 * minCostNeedBalance for each cost function instead of weights. We want to trigger balancing if any factor is out of balancer instead of trying to combine the factors in arbitrary weights. This makes operation and configuration much easier.
 * Simulated annealing to lower minCostNeedBalance periodically to unstuck the balancer from sub-optimum then gradually increase to keep the system stable. Also add cost of move as a counter measure for the decision [https://opensourcelibs.com/lib/tempest]
 * Orchestrated scheduling of compaction, normalizer and balancer
 * PID approach [https://www.amazon.com/dp/1449361692/ref=rdr_ext_tmb]



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