Charlie Qiangeng Xu created HBASE-17110:
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Summary: 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: 1.2.4, 2.0.0
Reporter: Charlie Qiangeng Xu
Assignee: Charlie Qiangeng Xu
This jira is about an enhancement of simpleLoadBalancer. Here we introduce a
new strategy: "bytableOverall" which could be controlled by adding:
<property>
<name>hbase.master.loadbalance.bytableOverall</name>
<value>true</value>
</property>
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 mode:
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 together.
If the pressures on different tables are different, the first byTable option is
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.
240 regions on server A but 410 regions on server B.
Consider this case, a cluster has 3 tables and 4 servers:
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.
>From the byTable strategy's perspective, the cluster has already been
>perfectly balanced on table level. But a perfect status should be like:
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
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 strategy.
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