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https://issues.apache.org/jira/browse/HBASE-14070?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16100734#comment-16100734
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Amit Patel commented on HBASE-14070:
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An additional issue to consider is what timestamp(s) to send over RPC for
syncing the clock(s) during events like region open/close. Since each region
server contains instances of each clock (system, system monotonic, hybrid
logical), it may be necessary/beneficial to send timestamps for each timestamp
type (physical and hybrid timestamp) and in turn update both corresponding
clocks upon receiving the timestamps. Otherwise we could send one timestamp
type and update one clock type if the clock type of meta and the target region
are the same, but send/update both if there was a mismatch in clock type.
> 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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