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https://issues.apache.org/jira/browse/HBASE-21476?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16708965#comment-16708965
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Sean Busbey commented on HBASE-21476:
-------------------------------------
{quote}
bq. What happens if a client that doesn't support nanoseconds attempts to write
to a table that is configured for nanoseconds?
There's no error of any sort unless
"base.hregion.keyvalue.timestamp.slop.millisecs" is specified. The value will
be stored at the millisecond timestamp. It's up to the client to be careful
here.
{quote}
Is there any way we could make this a hard enforcement? Maybe a new optional
way to flag that a client write has been done using nanoseconds? That way we
could detect an older client server side and send back an error instead of
trashing the data. Alternatively is there a point where we have both enough of
the RPC to know the client version and the request deserialized enough to know
the table where we could proactively reject operations from old clients?
If not, we'll need a big operator warning called out for the feature. Either
way we'll need something in the upgrade notes for whatever version this lands
in.
> 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: Apache HBase - Nanosecond Timestamps v1.pdf,
> nanosecond_timestamps_v1.patch, nanosecond_timestamps_v2.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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