[GitHub] [hbase] ragarkar commented on pull request #4799: HBASE-27389 Add cost function in balancer to consider the cost of bui…

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ragarkar commented on PR #4799:
URL: https://github.com/apache/hbase/pull/4799#issuecomment-1257548111

   > Mind explaining more about the algorithm here?
   > 
   > I guess the problem here is that, when moving a region from rs A to rs B, the block cache on A is useless now and then on rs B, we need to reload the block cache of this region, and it will evict other regions data?
   > 
   > What is the algo here to measure this cost?
   > 
   > Thanks.
   
   Hello,
   
   All the region servers maintain a list of all the HFiles which are already cached. This change was done as part of HBASE-27313.
   The current JIRA uses this information to find out the ratio of files already cached to the total number of files in the region server and puts this information in the region specific metric.
   
   The stochastic load balancer uses this information to find out the cost of moving a region from one region server to the other by comparing the ratio of files already prefetched. Higher the ratio of files prefetched on a region server, lower the cost of moving the region.


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