[jira] [Updated] (KUDU-1345) HybridClock can run backwards when clocks are far out of sync

["Jean-Daniel Cryans (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KUDU-1345?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jean-Daniel Cryans updated KUDU-1345:
-------------------------------------
    Fix Version/s: 0.7.1

> HybridClock can run backwards when clocks are far out of sync
> -------------------------------------------------------------
>
>                 Key: KUDU-1345
>                 URL: https://issues.apache.org/jira/browse/KUDU-1345
>             Project: Kudu
>          Issue Type: Bug
>    Affects Versions: 0.7.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>            Priority: Blocker
>             Fix For: 0.7.1, 0.8.0
>
>
> Nick Wolf reported an error he hit on his cluster where transactions were assigned out-of-order timestamps. After looking at his WALs for a while, I realized we have this bug:
> - the clock gets an update from another node a second in the future
> - we generate a lot of timestamps locally, which causes the clock to increment its logical portion
> - the logical portion exceeds the number of bits allocated to it (12 bits iirc). The way we return timestamps, this is OK -- we simply add the logical and physical portions, so it "wraps" into the physical portion, causing it to increment forward a few microseconds as we do thousands of writes.
> - however, our _host_ clock eventually reaches a higher value than the last physical portion. This causes us to reset our logical clock portion back to 1, which may actually rewind it back in time.



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