[jira] [Commented] (HBASE-21476) Support for nanosecond timestamps

["Sean Busbey (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-21476?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16686071#comment-16686071 ] 

Sean Busbey commented on HBASE-21476:
-------------------------------------

Please write a scope document. Consider emailing dev@hbase to gather feedback once you have one.

Important bits to cover:
* What use cases this enables
* How will this impact upgrades
* How/where we'll document this
* How we'll test this feature

Some example scope documents:
* [HBase Spark Integration|https://issues.apache.org/jira/secure/attachment/12878023/Apache%20HBase%20-%20Apache%20Spark%20Integration%20Scope%20-%20update%201.pdf] (HBASE-18405)
* [Read Replica Clusters|https://issues.apache.org/jira/secure/attachment/12888376/HBase%20Read-Replica%20Clusters%20Scope%20doc_v2.pdf] (HBASE-18477)

> Support for nanosecond timestamps
> ---------------------------------
>
>                 Key: HBASE-21476
>                 URL: https://issues.apache.org/jira/browse/HBASE-21476
>             Project: HBase
>          Issue Type: New Feature
>    Affects Versions: 2.1.1
>            Reporter: Andrey Elenskiy
>            Assignee: Andrey Elenskiy
>            Priority: Major
>              Labels: features, patch
>         Attachments: nanosecond_timestamps_v1.patch
>
>
> Introducing a new table attribute "NANOSECOND_TIMESTAMPS" to tell HBase to handle timestamps with nanosecond precision. This is useful for applications that timestamp updates at the source with nanoseconds and still want features like column family TTL and "hbase.hstore.time.to.purge.deletes" to work.
> The attribute should be specified either on new tables or on existing tables which have timestamps only with nanosecond precision. There's no migration from milliseconds to nanoseconds for already existing tables. We could add this migration as part of compaction if you think that would be useful, but that would obviously make the change more complex.
> I've added a new EnvironmentEdge method "currentTimeNano()" that uses [java.time.Instant|https://docs.oracle.com/javase/8/docs/api/java/time/Instant.html] to get time in nanoseconds which means it will only work with Java 8. The idea is to gradually replace all places where "EnvironmentEdge.currentTime()" is used to have HBase working purely with nanoseconds (which is a prerequisite for HBASE-14070). Also, I've refactored ScanInfo and PartitionedMobCompactor to expect TableDescriptor as an argument which makes code a little cleaner and easier to extend.
> Couple more points:
> - column family TTL (specified in seconds) and "hbase.hstore.time.to.purge.deletes" (specified in milliseconds) options don't need to be changed, those are adjusted automatically.
> - Per cell TTL needs to be scaled by clients accordingly after "NANOSECOND_TIMESTAMPS" table attribute is specified.
> Looking for everyone's feedback to know if that's a worthwhile direction. Will add more comprehensive tests in a later patch.



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