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From "Jonathan Gray (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-4527) Fix versioning such that every update is unique
Date Mon, 03 Oct 2011 23:32:34 GMT

    [ https://issues.apache.org/jira/browse/HBASE-4527?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13119747#comment-13119747
] 

Jonathan Gray commented on HBASE-4527:
--------------------------------------

Yeah, seems like we could utilize the memstoreTS once we solve those issues and then we don't
care about the timestamp being the same.  But we'd then have to expose RWCC to the API because
checkAndPut would need to specify it?  ugh
                
> Fix versioning such that every update is unique
> -----------------------------------------------
>
>                 Key: HBASE-4527
>                 URL: https://issues.apache.org/jira/browse/HBASE-4527
>             Project: HBase
>          Issue Type: Wish
>            Reporter: stack
>
> I wanted to use checkAndPut but there is a case where the check will not fail though
the cell has been updated: if a cell is update with exactly the value it had before, we'll
not know its been changed.  hbase-4507 did a checkAndPut where you could pass a timestamp
as part of the check so we'd check the cell value AND that the timestamp was the same.
> This would work in most regards but one; an update is done in the same millisecond. 
This is generally impossible but in a distributed system where clocks drift and a region can
be moved to a server whose clock is retarded, it is within the realm of possibilities that
it could happen.  So we should deal.
> One thought is that the version is made for sure unique.  We could make the timestamp
wider still so probability of the edits arriving within the same microsecond -- or whatever
it is that a double gives you -- would require us to run through a couple of billion universe
expand/contract cycles or we could have a monotonically increasing sequence id per millisecond.
> There could be some overlap between this issue and the persisting of rwcc to the filesystem
(though not currently as rwcc is implemented).

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