[HBASE-26147] Add dry run mode to hbase balancer

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 2.5.0, 3.0.0-alpha-2
• Component/s: Balancer, master
• Hadoop Flags: Reviewed

Release Note

This change adds new API to the Admin interface for triggering Region balancing on a cluster. A new BalanceRequest object was introduced which allows for configuring a dry run of the balancer (compute a plan without enacting it) and running the balancer in the presence of RITs. Corresponding API was added to the HBase shell as well.

• Assignee: Bryan Beaudreault
• Reporter: Bryan Beaudreault
• Created: 27/Jul/21 21:08
• Updated: 29/Dec/22 09:22
• Resolved: 02/Sep/21 02:08

Description

It's often rather hard to know how the cost function changes you're making will affect the balance of the cluster, and currently the only way to know is to run it. If the cost decisions are not good, you may have just moved many regions towards a non-ideal balance. Region moves themselves are not free for clients, and the resulting balance may cause a regression.

We should add a mode to the balancer so that it can be invoked without actually executing any plans. This will allow an administrator to iterate on their cost functions and used the balancer's logging to see how their changes would affect the cluster. 

Issue Links

• relates to: HBASE-26177 Add support to run balancer overriding current config
• relates to: RANGER-4029 Ranger cannot build with HBase 2.5.x versions because preBalance coprocessor hook syntax changed in HBASE-26147
• relates to: HBASE-25697 StochasticBalancer improvement for large scale clusters
• links to: GitHub Pull Request #3536
• links to: GitHub Pull Request #3630

Sub-Tasks

• Set BalanceRequest$Builder to InterfaceAudience.Private: Resolved
• Revert 26240, Apply InterfaceAudience.Private to BalanceResponse$Builder: Resolved