[jira] [Created] (HIVE-21376) Incompatible change in Hive bucket computation

["David Phillips (JIRA)" <ji...@apache.org>]

David Phillips created HIVE-21376:
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             Summary: Incompatible change in Hive bucket computation
                 Key: HIVE-21376
                 URL: https://issues.apache.org/jira/browse/HIVE-21376
             Project: Hive
          Issue Type: Bug
    Affects Versions: 3.1.0
            Reporter: David Phillips


HIVE-20007 seems to have inadvertently changed the bucket hash code computation via {{ObjectInspectorUtils.getBucketHashCodeOld()}} for the {{DATE}} and {{TIMESTAMP}} data type2.

{{DATE}} was previously computed using {{DateWritable}}, which uses {{daysSinceEpoch}} as the hash code. It is now computed using {{DateWritableV2}}, which uses the hash code of {{java.time.LocalDate}} (which is not days since epoch).

{{TIMESTAMP}} was previous computed using {{TimestampWritable}} and now uses {{TimestampWritableV2}}. They ostensibly use the same hash code computation, but there are two important differences:
 # {{TimestampWritable}} rounds the number of milliseconds into the seconds portion of the computation, but {{TimestampWritableV2}} does not.
 # {{TimestampWritable}} gets the epoch time from {{java.sql.Timestamp}}, which returns it relative to the JVM time zone, not UTC. {{TimestampWritableV2}} uses a {{LocalDateTime}} relative to UTC.

I was unable to get Hive 3.1 running in order to verify if this actually causes data to be read or written incorrectly (there may be code above this library method which makes things work correctly). However, if my understanding is correct, this means Hive 3.1 is both forwards and backwards incompatible with bucketed tables using either of these data types. It also indicates that Hive needs tests to verify that the hash code does not change between releases.



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