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https://issues.apache.org/jira/browse/HBASE-14949?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15137089#comment-15137089
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Phil Yang commented on HBASE-14949:
-----------------------------------

I think we needn't wait for upgrading finished. If we solve this issue in 
version A, and use new WAL logic in version B. We can only support rolling 
upgrade to version B if the old version >=A.  So if there is a RS with version 
B, all RSs in the cluster will contain this patch.

> Skip duplicate entries when replay WAL.
> ---------------------------------------
>
>                 Key: HBASE-14949
>                 URL: https://issues.apache.org/jira/browse/HBASE-14949
>             Project: HBase
>          Issue Type: Sub-task
>            Reporter: Heng Chen
>         Attachments: HBASE-14949.patch, HBASE-14949_v1.patch, 
> HBASE-14949_v2.patch
>
>
> As HBASE-14004 design,  there will be duplicate entries in different WAL.  It 
> happens when one hflush failed, we will close old WAL with 'acked hflushed' 
> length,  then open a new WAL and write the unacked hlushed entries into it.
> So there maybe some overlap between old WAL and new WAL.
> We should skip the duplicate entries when replay.  I think it has no harm to 
> current logic, maybe we do it first. 



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