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https://issues.apache.org/jira/browse/HBASE-21487?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16708402#comment-16708402
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Bhupendra Kumar Jain commented on HBASE-21487:
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{quote}record the seqenceID of the current tabledescriptor on FS(and pass to 
ModifyTableProcedure),
{quote}
I think , SequenceID concept is specific to FSTableDescriptors implementation 
which is one of the impl of TableDescriptors interface. So IMO we should not 
depend on sequenceID here for comparison.  

May be we can  pass the old_table_descriptor also in ModifyTableProcedure. In 
MODIFY_TABLE_PREPARE step, we can compare the old_table_descriptor with 
current_table_descriptor, if they are not same then we can throw exception ... 




> Concurrent modify table ops can lead to unexpected results
> ----------------------------------------------------------
>
>                 Key: HBASE-21487
>                 URL: https://issues.apache.org/jira/browse/HBASE-21487
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 3.0.0, 2.0.0
>            Reporter: Syeda Arshiya Tabreen
>            Priority: Major
>
> Concurrent  modifyTable or add/delete/modify columnFamily leads to incorrect 
> result. After HBASE-18893, The behavior of add/delete/modify column family 
> during concurrent operation is changed compare to branch-1.When  one client 
> is adding cf2 and another one cf3 .. In branch-1 final result will be 
> cf1,cf2,cf3 but now either cf1,cf2 OR cf1,cf3 will be the outcome depending 
> on which ModifyTableProcedure executed finally.Its because new table 
> descriptor is constructed before submitting the ModifyTableProcedure in 
> HMaster class and its not guarded by any lock.
> *Steps to reproduce*
> 1.Create table 't' with column family 'f1'
> 2.Client-1 and Client-2 requests to add column family 'f2' and 'f3' on table 
> 't' concurrently.
> *Expected Result*
> Table should have three column families(f1,f2,f3)
> *Actual Result*
> Table 't' will have column family either (f1,f2) or (f1,f3)



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