[HBASE-26988] Balancer should reset to default setting for hbase.master.loadbalance.bytable if dynamically reloading configuration

• Type: Bug
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 3.0.0-alpha-1, 2.0.0
• Fix Version/s: 2.5.0, 3.0.0-alpha-3
• Component/s: Balancer
• Hadoop Flags: Reviewed
• Assignee: David Manning
• Reporter: David Manning
• Created: 29/Apr/22 04:22
• Updated: 01/May/22 05:13
• Resolved: 29/Apr/22 22:54

Description

1. Set hbase.master.loadbalance.bytable to true in hbase-site.xml
2. Start HMaster
3. Remove hbase.master.loadbalance.bytable entry in hbase-site.xml
4. Dynamically reload configuration for hmaster (https://hbase.apache.org/book.html#dyn_config)

Expected: load balancing would no longer happen by table
Actual: load balancing still happens by table
Workaround: leave the entry in hbase-site.xml but explicitly set to false

Note 1: The steps may only work if the config value is not in hbase-default.xml so it may be an unlikely scenario.

Note 2: I see this when running tests added in HBASE-22349, depending on the order of execution of test methods. If testSloppyTablesLoadBalanceByTable executes before testBalanceOfSloppyServers there will be a failure. We could apply the workaround to the tests (explicitly set to false), but it seems better to fix the dynamic reconfiguration behavior. Regardless, I will propose test fixes in HBASE-26989.

Issue Links

• Discovered while testing: HBASE-22349 Stochastic Load Balancer skips balancing when node is replaced in cluster
• is related to: HBASE-26989 TestStochasticLoadBalancer has some slow methods, and inconsistent set, reset, unset of configuration
• links to: GitHub Pull Request #4384