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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-14070) Hybrid Logical Clocks for HBase
Date Sun, 23 Jul 2017 08:04:02 GMT

    [ https://issues.apache.org/jira/browse/HBASE-14070?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16097545#comment-16097545
] 

stack commented on HBASE-14070:
-------------------------------

Having to manage catch-up is 'known issue' that has had some consideration. If skew too large
or we are unable to catch-up given allotted logical time per ms, let the RS just fail (in
first implementation).

On Problem 1: this will just become a case of a server being off by 30 seconds which currently
results in a RS shutdown.
On Problem 2: yeah, should add in protection. We can do this in-the-small in the time-engine
unit tests?
On Problem 3: is not a problem?

 

> Hybrid Logical Clocks for HBase
> -------------------------------
>
>                 Key: HBASE-14070
>                 URL: https://issues.apache.org/jira/browse/HBASE-14070
>             Project: HBase
>          Issue Type: New Feature
>            Reporter: Enis Soztutar
>            Assignee: Amit Patel
>         Attachments: HBASE-14070.master.001.patch, HybridLogicalClocksforHBaseandPhoenix.docx,
HybridLogicalClocksforHBaseandPhoenix.pdf
>
>
> HBase and Phoenix uses systems physical clock (PT) to give timestamps to events (read
and writes). This works mostly when the system clock is strictly monotonically increasing
and there is no cross-dependency between servers clocks. However we know that leap seconds,
general clock skew and clock drift are in fact real. 
> This jira proposes using Hybrid Logical Clocks (HLC) as an implementation of hybrid physical
clock + a logical clock. HLC is best of both worlds where it keeps causality relationship
similar to logical clocks, but still is compatible with NTP based physical system clock. HLC
can be represented in 64bits. 
> A design document is attached and also can be found here: 
> https://docs.google.com/document/d/1LL2GAodiYi0waBz5ODGL4LDT4e_bXy8P9h6kWC05Bhw/edit#



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