huginn created HBASE-30385:
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Summary: Avoid scheduling duplicate system region moves
Key: HBASE-30385
URL: https://issues.apache.org/jira/browse/HBASE-30385
Project: HBase
Issue Type: Bug
Components: master
Affects Versions: 2.4.11
Reporter: huginn
When a newer-version RegionServer joins a mixed-version cluster,
AssignmentManager.checkIfShouldMoveSystemRegionAsync() can schedule the same
non-meta system-region move more than once when multiple excluded servers are
processed.
The method accumulates RegionPlans in a list while iterating excluded servers,
but currently iterates over the accumulated list inside that same loop. A plan
collected from an earlier server is therefore submitted again when the next
excluded server is processed. The second submission can hit the in-transition
guard and emit an exception such as:
{code}
... is currently in transition; pid=...
{code}
This can also prevent the remaining plans from being submitted.
The fix is to submit the collected plans after the server loop, and use
plan.getSource() in the log so the source server matches the plan.
Reproduction and validation:
* Use a mixed-version cluster with at least two excluded servers containing
system regions.
* Source review against Apache master identifies the duplicated iteration.
* No unit test is included; this is a small control-flow and logging correction.
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