Hi, I recently worked on improving region normalization feature. If region split request triggered by the execution of SplitNormalizationPlan fails, there is no way of knowing whether the failed split originated from region normalization. Such association would give RegionNormalizer information so that it can make better normalization decisions in the subsequent invocations.
One enhancement I can think of is to embed metadata in SplitRequest which gets passed through RegionStateTransitionContext when RegionServerServices#reportRegionStateTransition() is called. This way, RegionStateListener can be notified with the metadata (id of the requester). Comment is welcome.
