[jira] Commented: (HBASE-2486) Add simple "anti-entropy" for region assignment

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    [ https://issues.apache.org/jira/browse/HBASE-2486?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12861215#action_12861215 ] 

stack commented on HBASE-2486:
------------------------------

This don't look too hard too do.  I was thinking that we need to make sure that 3a and 3b don't have holes but if a 3c, then then we'll find them the quicker.

Doing Todd' technique above would invalidate need for HBASE-1920?

> Add simple "anti-entropy" for region assignment
> -----------------------------------------------
>
>                 Key: HBASE-2486
>                 URL: https://issues.apache.org/jira/browse/HBASE-2486
>             Project: Hadoop HBase
>          Issue Type: Improvement
>          Components: master, regionserver
>    Affects Versions: 0.20.5
>            Reporter: Todd Lipcon
>             Fix For: 0.20.5
>
>
> We've seen a number of bugs where a region server thinks it should not be serving a region, but the master and META think it should be. I'd like to propose a very simple way of fixing this issue:
> 1) whenever a regionserver throws a NotServingRegionException, it also marks that region id in an RS-wide Set
> 2) when a region sends a heartbeat, include a message for each of these regions, MSG_REPORT_NSRE or somesuch, and then clear the set
> 3) when the master receives MSG_REPORT_NSRE, it does the following checks:
> a) if the region is assigned elsewhere according to META, the NSRE was due to a stale client, ignore
> b) if the region is in transition, ignore
> c) otherwise, we have an inconsistency, and we should take some steps to resolve (eg mark the region unassigned, or exit the master if we are in "paranoid mode")
> Whatever we do, we need to make sure that this is loudly logged, and causes unit tests to fail, when it's detected. This should *not* happen, but when it does, it would be good to recover without addtable.rb, etc.

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