[HBASE-10528] DefaultBalancer selects plans to move regions onto draining nodes

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.94.5
• Fix Version/s: 1.0.0, 0.98.10, 1.1.0, 0.94.27
• Hadoop Flags: Reviewed
• Assignee: churro morales
• Reporter: churro morales
• Created: 14/Feb/14 01:46
• Updated: 06/Apr/18 17:54
• Resolved: 15/Jan/15 21:19

Description

We have quite a large cluster > 100k regions, and we needed to isolate a region was very hot until we could push a patch. We put this region on its own regionserver and set it in the draining state. The default balancer was selecting regions to move to this cluster for its region plans.

It just so happened for other tables, the default load balancer was creating plans for the draining servers, even though they were not available to move regions to. Thus we were closing regions, then attempting to move them to the draining server then finding out its draining.

We had to disable the balancer to resolve this issue.

There are some approaches we can take here.

1. Exclude draining servers altogether, don't even pass those into the load balancer from HMaster.

2. We could exclude draining servers from ceiling and floor calculations where we could potentially skip load balancing because those draining servers wont be represented when deciding whether to balance.

3. Along with #2 when assigning regions, we would skip plans to assign regions to those draining servers.

I am in favor of #1 which is simply removes servers as candidates for balancing if they are in the draining state.

But I would love to hear what everyone else thinks.

Issue Links

• relates to: HBASE-12843 TestAssignmentManager.testOpenCloseRegionRPCIntendedForPreviousServer failing frequently in 0.98 builds