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From "Ted Yu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-17110) Add an "Overall Strategy" option(balanced both on table level and server level) to SimpleLoadBalancer
Date Wed, 16 Nov 2016 17:45:58 GMT

    [ https://issues.apache.org/jira/browse/HBASE-17110?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15671108#comment-15671108

Ted Yu commented on HBASE-17110:

The config should be on by default.
+    private int initialnumRegions;
Why do we need the above variable ? Can this be deduced from size of hriList ?
+    public BalanceInfo(int nextRegionForUnload, int numRegionsAdded, int initialnumRegions,
List<HRegionInfo> hriList) {
+    int getinitialnumRegions() {
Upper case 'i' of initial and 'n' of num - same with variable name.
+  private List<ServerAndLoad> ServerLoadList;
Lower case the leading 'S'.
+    if (sdv > avgLoadOverall / 10) return true;
How is the constant of 10 determined ?
+    // But if we need to balanceoverall, we should skip assigning those regions here and
assign them along with other
+    // regions( that would be peeled off from RS that has max num of regions) in the following
needsBalanceOverall logic
Wrap long line.

> Add an "Overall Strategy" option(balanced both on table level and server level) to SimpleLoadBalancer
> -----------------------------------------------------------------------------------------------------
>                 Key: HBASE-17110
>                 URL: https://issues.apache.org/jira/browse/HBASE-17110
>             Project: HBase
>          Issue Type: New Feature
>          Components: Balancer
>    Affects Versions: 2.0.0, 1.2.4
>            Reporter: Charlie Qiangeng Xu
>            Assignee: Charlie Qiangeng Xu
>         Attachments: HBASE-17110.patch, SimpleBalancerBytableOverall.V1
> This jira is about an enhancement of simpleLoadBalancer. Here we introduce a new strategy:
"bytableOverall" which could be controlled by adding:
> {noformat}
> <property>
>   <name>hbase.master.loadbalance.bytableOverall</name>
>   <value>true</value>
> </property>
> {noformat}
> We have been using the strategy on our largest cluster for several months. it's proven
to be very helpful and stable, especially, the result is quite visible to the users.
> Here is the reason why it's helpful:
> When operating large scale clusters(our case), some companies still prefer to use {{SimpleLoadBalancer}}
due to its simplicity, quick balance plan generation, etc. Current SimpleLoadBalancer has
two modes: 
> 1. byTable, which only guarantees that the regions of one table could be uniformly distributed.

> 2. byCluster, which ignores the distribution within tables and balance the regions all
> If the pressures on different tables are different, the first byTable option is the preferable
one in most case. Yet, this choice sacrifice the cluster level balance and would cause some
servers to have significantly higher load, e.g. 242 regions on server A but 417 regions on
server B.(real world stats)
> Consider this case,  a cluster has 3 tables and 4 servers:
> {noformat}
>   server A has 3 regions: table1:1, table2:1, table3:1
>   server B has 3 regions: table1:2, table2:2, table3:2
>   server C has 3 regions: table1:3, table2:3, table3:3
>   server D has 0 regions.
> {noformat}
> From the byTable strategy's perspective, the cluster has already been perfectly balanced
on table level. But a perfect status should be like:
> {noformat}
>   server A has 2 regions: table2:1, table3:1
>   server B has 2 regions: table1:2, table3:2
>   server C has 3 regions: table1:3, table2:3, table3:3
>   server D has 2 regions: table1:1, table2:2
> {noformat}
> We can see the server loads change from 3,3,3,0 to 2,2,3,2, while the table1, table2
and table3 still keep balanced.   
> And this is what the new mode "byTableOverall" can achieve.
> Two UTs have been added as well and the last one demonstrates the advantage of the new
> Also, a onConfigurationChange method has been implemented to hot control the "slop" variable.

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