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https://issues.apache.org/jira/browse/HBASE-4527?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13119756#comment-13119756
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Jonathan Gray commented on HBASE-4527:
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Agreed.
> 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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