[jira] [Comment Edited] (HBASE-8741) Mutations on Regions in recovery mode might have same sequenceIDs

["stack (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-8741?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13730755#comment-13730755 ] 

stack edited comment on HBASE-8741 at 8/6/13 1:28 PM:
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Region is redundant in RegionSequenceIds since SequenceIds are per Region always when this patch applied.
                
      was (Author: stack):
    I Region redundant in RegionSequenceIds since SequenceIds are per Region always when this patch applied.
                  
> Mutations on Regions in recovery mode might have same sequenceIDs
> -----------------------------------------------------------------
>
>                 Key: HBASE-8741
>                 URL: https://issues.apache.org/jira/browse/HBASE-8741
>             Project: HBase
>          Issue Type: Bug
>          Components: MTTR
>    Affects Versions: 0.95.1
>            Reporter: Himanshu Vashishtha
>            Assignee: Himanshu Vashishtha
>             Fix For: 0.95.2
>
>         Attachments: HBASE-8741-v0.patch, HBASE-8741-v2.patch, HBASE-8741-v3.patch, HBASE-8741-v4-again.patch, HBASE-8741-v4-again.patch, HBASE-8741-v4.patch
>
>
> Currently, when opening a region, we find the maximum sequence ID from all its HFiles and then set the LogSequenceId of the log (in case the later is at a small value). This works good in recovered.edits case as we are not writing to the region until we have replayed all of its previous edits. 
> With distributed log replay, if we want to enable writes while a region is under recovery, we need to make sure that the logSequenceId > maximum logSequenceId of the old regionserver. Otherwise, we might have a situation where new edits have same (or smaller) sequenceIds. 
> We can store region level information in the WALTrailer, than this scenario could be avoided by:
> a) reading the trailer of the "last completed" file, i.e., last wal file which has a trailer and,
> b) completely reading the last wal file (this file would not have the trailer, so it needs to be read completely).
> In future, if we switch to multi wal file, we could read the trailer for all completed WAL files, and reading the remaining incomplete files.

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