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From "Enis Soztutar (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-14070) Hybrid Logical Clocks for HBase
Date Fri, 15 Jul 2016 18:31:20 GMT

    [ https://issues.apache.org/jira/browse/HBASE-14070?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15379859#comment-15379859
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Enis Soztutar commented on HBASE-14070:
---------------------------------------

There were 2 issues before. 1 was the case you mentioned that, and the other is that a regionserver's
local clock can be behind so that the update to meta is eclipsed by earlier puts with higher
timestamp. With new master code, all operations to meta are strictly serialized by the master.
The regionservers never update meta themselves. So delere-after-put should not be a problem
if master guarantees that delete RPC is finished before the put RPC is sent. 

> 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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