Biju Nair created HBASE-22265:
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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}
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