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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8763) [BRAINSTORM] Combine MVCC and SeqId
Date Thu, 01 May 2014 05:11:15 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8763?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13986354#comment-13986354
] 

stack commented on HBASE-8763:
------------------------------

(Pardon me; am excited about this one so went back to do some more study...)

So yeah, why do a MutableLong in KV rather than just a volatile?  Probably same in the end...
 I see you want to get a reference to a KV.  You trying to tie a KV to something else in case
the mvcc gets updated?

Maybe this is it:

-    newKv.setMvccVersion(kv.getMvccVersion());
+    newKv.setMvccVersion(kv.getMvccVersionReference());

We are cloning.  The original gets updated later?  You want to make sure clone is updated
too?

Would be cool if we could get rid of this clone one day.



> [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
>            Assignee: Jeffrey Zhong
>            Priority: Critical
>         Attachments: hbase-8736-poc.patch, hbase-8763-poc-v1.patch, hbase-8763_wip1.patch
>
>
> 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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