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From "Sai Teja Ranuva (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-14070) Hybrid Logical Clocks for HBase
Date Thu, 14 Jul 2016 21:26:20 GMT

    [ https://issues.apache.org/jira/browse/HBASE-14070?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15378417#comment-15378417
] 

Sai Teja Ranuva commented on HBASE-14070:
-----------------------------------------

[~enis] 
Referring to description in RB link - "TTL works with HLC timestamps and SYSTEM timestamps".

I feel TTL might not work well with HLC, as there could be a message with much greater PT
than the current system time, say a second (but less than max delta we set), which can take
the HLC physical time forward. If you read the time the HLC time before the message was received
and after the message was received, the difference will be inflated by one second. 
Can you clarity this aspect ?


> 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: Sai Teja Ranuva
>         Attachments: 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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