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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8741) Mutations on Regions in recovery mode might have same sequenceIDs
Date Tue, 06 Aug 2013 05:53:49 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8741?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13730397#comment-13730397
] 

stack commented on HBASE-8741:
------------------------------

Yeah, does not look like it is up on rb.  Its 100k.

Is the formatting off here?

{code}
-              + "] - WAL is going away");
-          return false;
+            + "] - WAL is going away");
+        return false;
         }
{code}

Is HLogServices the right name for the Interface that has obtainRegionsSequenceId?  Should
it be SequenceIdsService?  Or just SequenceIds?  It is HLog that wants the Service, right?
 It is not a a Service that HLog is providing?

What else has changed in this patch since previous verions?  Thanks H.

It is probably time for someone else to review this one.  Any takers?   Makes for nice cleanup
of sequenceid reasoning.
                
> 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
>         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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