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https://issues.apache.org/jira/browse/HBASE-18105?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16148406#comment-16148406
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stack commented on HBASE-18105:
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bq. ...but still not clear about why this PONR could happen
IIRC, there were holy mary moments where if update to meta failed because
hosting server crashed, then we'd be in an unknown state; the regions had been
split but the fact was not recorded up in hbase:meta.
For AMv2, there is no AMv2 since we will record what step we are at and
post-crash will rerun the step we were at when machine went down (each step is
supposed to be idempotent).
You need more [~easyliangjob]? Just say.
> [AMv2] Split/Merge need cleanup; currently they diverge and do not fully
> embrace AMv2 world
> -------------------------------------------------------------------------------------------
>
> Key: HBASE-18105
> URL: https://issues.apache.org/jira/browse/HBASE-18105
> Project: HBase
> Issue Type: Sub-task
> Components: Region Assignment
> Affects Versions: 2.0.0
> Reporter: stack
> Fix For: 2.0.0
>
>
> Region Split and Merge work on the new AMv2 but they work differently. This
> issue is about bringing them back together and fully embracing the AMv2
> program.
> They both have issues mostly the fact that they carry around baggage no
> longer necessary in the new world of assignment.
> Here are some of the items:
> Split and Merge metadata modifications are done by the Master now but we have
> vestige of Split/Merge on RS still; e.g. when we SPLIT, we ask the Master
> which asks the RS, which turns around, and asks the Master to run the
> operation. Fun. MERGE is all done Master-side.
>
> Clean this up. Remove asking RS to run SPLIT and remove RegionMergeRequest,
> etc. on RS-side. Also remove PONR. We don’t Points-Of-No-Return now we are up
> on Pv2. Remove all calls in Interfaces; they are unused. Make RS still able
> to detect when split, but have it be a client of Master like anyone else.
> Split is Async but does not return procId
> Split is async. Doesn’t return the procId though. Merge does. Fix. Only hard
> part here I think is the Admin API does not allow procid return.
> Flags
> Currently OFFLINE is determined by looking either at the master instance of
> HTD (isOffline) and/or at the RegionState#state. Ditto for SPLIT. For MERGE,
> we rely on RegionState#state. Related is a note above on how split works --
> there is a split flag in HTD when there should not be.
>
> TODO is move to rely on RegionState#state exclusively in Master.
> From Split/Merge Procedures need finishing in
> https://docs.google.com/document/d/1eVKa7FHdeoJ1-9o8yZcOTAQbv0u0bblBlCCzVSIn69g/edit#heading=h.4b60dc1h4m1f
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