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https://issues.apache.org/jira/browse/HBASE-14070?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16142478#comment-16142478
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Amit Patel commented on HBASE-14070:
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Just as a status update, I'll be finishing my internship so I will be much less
active in the future. I am extremely grateful for the help and support that I
have received from the community. At the moment there are still a few
outstanding issues that should be addressed before merging the work into master:
* Performance of HLC (Clock#now, Clock#update are expensive, not as big of an
issue if HLC is only used for meta but certainly is for user tables)
* Huge number of tests timing out in in the pre-commit/[public
branch|https://builds.apache.org/job/HBASE-14070.HLC/] builds (but haven't been
able to replicate the test time-out and they pass just fine if ran locally)
In terms of enabling HLC on user tables, remaining issues would include:
* Some tests that are still explicitly setting the timestamp and need to be
converted to instead manipulate the current time via mocking the clocks
* Bulk load does not update the HLC
Some additional brainstorming/discussions includes:
* [Deprecate setting of timestamp in client for
HLC|https://issues.apache.org/jira/browse/HBASE-18642]
* [Add 'Transaction ID' to Result for
HLC|https://issues.apache.org/jira/browse/HBASE-18643]
> 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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