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https://issues.apache.org/jira/browse/IMPALA-8180?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Quanlong Huang updated IMPALA-8180:
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Fix Version/s: (was: Impala 4.0)
> Change Kudu timestamp writer to round towards minus infinity
> ------------------------------------------------------------
>
> Key: IMPALA-8180
> URL: https://issues.apache.org/jira/browse/IMPALA-8180
> Project: IMPALA
> Issue Type: New Feature
> Components: Backend
> Affects Versions: Impala 3.1.0
> Reporter: Csaba Ringhofer
> Priority: Minor
>
> Kudu timestamps are microseconds since Unix epoch stored as int64, so Impala
> has to round its nanosecond timestamps before writing them to Kudu tables.
> Currently this is done by rounding to the nearest microsecond. Meanwhile Hive
> uses rounding towards minus infinity when reducing the precision of
> timestamps, which is a better way in my opinion, because it cannot move a
> timestamp into a different day, and should be also a bit faster.
> Changing the rounding method is breaking change, so I would only do this in
> the next major release.
> Example:
> create table tkudu (id int primary key, t timestamp) stored as kudu;
> insert into tkudu values
> (1,"1970-01-01 00:00:00.1111111"), -- all sub-second parts are 7 digit
> (2,"1970-01-01 23:59:59.9999999"),
> (3,"1969-12-31 23:59:59.9999999");
> select * from tkudu;
> This currently returns:
> 1,1970-01-01 00:00:00.111111000
> 2,1970-01-02 00:00:00
> 3,1970-01-01 00:00:00
> 1 was rounded down to microsec precision, while 2 and 3 were rounded up and
> also stepped to another day.
> If the table was written using rounding toward minus infinity, then the query
> would return this:
> 1,1970-01-01 00:00:00.111111000
> 2,1970-01-01 23:59:59.999999000
> 3,1969-12-31 23:59:59.999999000
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