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https://issues.apache.org/jira/browse/HBASE-3663?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13008069#comment-13008069
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Ted Yu commented on HBASE-3663:
-------------------------------
Sloppiness is gone in trunk.
Also, I only found one call to ceil() in LoadBalancer.
{code}
int max = (int)Math.ceil((float)numRegions/numServers);
{code}
> The starvation problem in current load balance algorithm
> --------------------------------------------------------
>
> Key: HBASE-3663
> URL: https://issues.apache.org/jira/browse/HBASE-3663
> Project: HBase
> Issue Type: Bug
> Reporter: Liyin Tang
> Attachments: result_new_load_balance.txt, result_old_load_balance.txt
>
>
> This is an interesting starvation case. There are 2 conditions to trigger
> this problem.
> Condition1: r/s - r/(s+1) << 1
> Let r: the number of regions
> Let s: the number of servers
> Condition2: for each server, the load of each server is less or equal the
> ceil of avg load.
> Here is the unit test to verify this problem:
> For example, there are 16 servers and 62 regions. The avg load is
> 3.875. And setting the slot to 0 to keep the load of each server either 3 or
> 4.
> When a new server is coming, no server needs to assign regions to this new
> server, since no one is larger the ceil of the avg.
> (Setting slot to 0 is to easily trigger this situation, otherwise it needs
> much larger numbers)
> Solutions is pretty straightforward. Just compare the floor of the avg
> instead of the ceil. This solution will evenly balance the load from the
> servers which is little more loaded than others.
> I also attached the comparison result for the case mentioned above between
> the old balance algorithm and new balance algorithm. (I set the slot = 0 when
> testing)
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