[jira] [Created] (HBASE-17178) Add region balance throttling

["Guanghao Zhang (JIRA)" <ji...@apache.org>]

Guanghao Zhang created HBASE-17178:
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             Summary: Add region balance throttling
                 Key: HBASE-17178
                 URL: https://issues.apache.org/jira/browse/HBASE-17178
             Project: HBase
          Issue Type: Improvement
          Components: Balancer
            Reporter: Guanghao Zhang


Our online cluster serves dozens of  tables and different tables serve for different services. If the balancer moves too many regions in the same time, 
it will decrease the availability for some table or some services. So we add region balance throttling on our online serve cluster. 
We introduce a new config hbase.balancer.max.balancing.regions, which means the max number of regions in transition when balancing.
If we config this to 1 and a table have 100 regions, then the table will have 99 regions available at any time. It helps a lot for our use case and it has been running a long time
our production cluster.

But for some use case, we need the balancer run faster. If a cluster has 100 regionservers, then it add 50 new regionservers for peak requests. Then it need balancer run as soon as
possible and let the cluster reach a balance state soon. Our idea is compute max number of regions in transition by the max balancing time and the average time of region in transition.
Then the balancer use the computed value to throttling.

Examples for understanding.
A cluster has 100 regionservers, each regionserver has 200 regions and the average time of region in transition is 1 seconds, we config the max balancing time is 10 * 60 seconds.
Case 1. One regionserver crash, the cluster at most need balance 200 regions. Then 200 / (10 * 60s / 1s) < 1, it means the max number of regions in transition is 1 when balancing. Then the balancer can move region one by one and the cluster will have high availability  when balancing.
Case 2. Add other 100 regionservers, the cluster at most need balance 10000 regions. Then 10000 / (10 * 60s / 1s) = 16.7, it means the max number of regions in transition is 17 when balancing. Then the cluster can reach a balance state within the max balancing time.

Any suggestions are welcomed.



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