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Jesus Camacho Rodriguez commented on HIVE-21376:
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Thanks for reporting this [~electrum]. Indeed this should be an issue with
versions >= 3.1. I believe this also means that old implementation could lead
to data ending up in wrong buckets when users were reading/writing in different
time zones.
There is a bucketing version property associated with tables that is used to
keep backwards compatibility introduced in HIVE-18910. Only two versions exist
at this time, v1 and v2, each of them using different hash functions. v1 relies
on {{getBucketHashCodeOld}} as you mention. {{getBucketHashCodeOld}} should be
changed so v1 can compute hashcode for {{Date}} and {{Timestamp}} values as it
used to do. I think v2 can remain unchanged.
> 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
> Priority: Major
>
> 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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