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https://issues.apache.org/jira/browse/PHOENIX-4759?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16496183#comment-16496183
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Sergey Soldatov commented on PHOENIX-4759:
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That's well reproduced on 5.x branch, but may (should) affect master branch 
under certain circumstances. The SYSTEM.CATALOG region get stuck during open 
operation because there are 2 concurrent open region threads that are trying to 
load system tables. 
Loading sequence:
Thread 1:
MetaDataEndpointImpl -> PhoenixDatabaseMetaData -- (trying to load 
QueryConstants)
Thread 2:
MetaDataRegionObserver -> QueryConstants -> TableProperty -> SQLExceptionCode 
-> (trying to load PhoenixDatabaseMetaData)
Since only one thread is capable to load class and second thread is already 
loading QueryConstants and first thread is loading PhoenixDatabaseMetaData , we 
have a dead lock. 
We can break this by removing the dependency between SQLExceptionCode and 
PhoenixDatabaseMetaData.



> During restart RS that hosts SYSTEM.CATALOG table may get stuck
> ---------------------------------------------------------------
>
>                 Key: PHOENIX-4759
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-4759
>             Project: Phoenix
>          Issue Type: Bug
>    Affects Versions: 4.14.0, 5.0.0
>            Reporter: Romil Choksi
>            Assignee: Sergey Soldatov
>            Priority: Blocker
>             Fix For: 4.14.0, 5.0.0
>
>
> Sometimes when a cluster has restarted the regions that belong to 
> SYSTEM.CATALOG and other system tables on the same RS may be stuck in RiT. 



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