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From "Sergey Shelukhin (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8763) [BRAINSTORM] Combine MVCC and SeqId
Date Mon, 08 Jul 2013 21:19:48 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8763?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13702436#comment-13702436
] 

Sergey Shelukhin commented on HBASE-8763:
-----------------------------------------

I have another idea, related to this, that intends to solve problems with clock skew also.
If user doesn't supply ts, we can also combine ts with seqId and mvcc :) That way conflicts
due to clock skew won't happen assuming seqId doesn't go back; which it doesn't under current
assumptions such as compactions and log recovery.
If user does, we can store user ts and seqId or just user ts (but then user has to avoid conflicts,
same as now).
This makes mixed scenarios more difficult though, and some people may rely in default ts actually
storing time.
                
> [BRAINSTORM] Combine MVCC and SeqId
> -----------------------------------
>
>                 Key: HBASE-8763
>                 URL: https://issues.apache.org/jira/browse/HBASE-8763
>             Project: HBase
>          Issue Type: Improvement
>          Components: regionserver
>            Reporter: Enis Soztutar
>             Fix For: 0.98.0
>
>
> HBASE-8701 and a lot of recent issues include good discussions about mvcc + seqId semantics.
It seems that having mvcc and the seqId complicates the comparator semantics a lot in regards
to flush + WAL replay + compactions + delete markers and out of order puts. 
> Thinking more about it I don't think we need a MVCC write number which is different than
the seqId. We can keep the MVCC semantics, read point and smallest read points intact, but
combine mvcc write number and seqId. This will allow cleaner semantics + implementation +
smaller data files. 
> We can do some brainstorming for 0.98. We still have to verify that this would be semantically
correct, it should be so by my current understanding.

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