Biju Nair created HBASE-22265: --------------------------------- Summary: Cost calculation in SLB may not be correct Key: HBASE-22265 URL: https://issues.apache.org/jira/browse/HBASE-22265 Project: HBase Issue Type: Brainstorming Components: Balancer Reporter: Biju Nair
In [CostFromArray|https://github.com/apache/hbase/blob/baf3ae80f5588ee848176adefc9f56818458a387/hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/StochasticLoadBalancer.java#L1039] method of SLB, the calculated value of {{max}} which in turn used to scale "may" not be correct. {noformat} // Compute max as if all region servers had 0 and one had the sum of all costs. This must be // a zero sum cost for this to make sense. double max = ((count - 1) * mean) + (total - mean);{noformat} with the current calculation {{max}} will end up with the value close to twice that of the total of all the elements passed in the array (less the mean value) while the comment above the calculation seem to imply that the {{max}} value to be sum of all costs i.e. the value of the variable {{total}}. Also it would be good to document the reasoning for the following calculation in the same method. I can create a patch if anyone who is familiar with this code can help understand the reasoning. {noformat} min = (numHigh * (Math.ceil(mean) - mean)) + (numLow * (mean - Math.floor(mean)));{noformat} -- This message was sent by Atlassian JIRA (v7.6.3#76005)