[jira] [Assigned] (HIVE-21290) Restore historical way of handling timestamps in Parquet while keeping the new semantics at the same time

["Karen Coppage (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HIVE-21290?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Karen Coppage reassigned HIVE-21290:
------------------------------------

    Assignee: Karen Coppage

> Restore historical way of handling timestamps in Parquet while keeping the new semantics at the same time
> ---------------------------------------------------------------------------------------------------------
>
>                 Key: HIVE-21290
>                 URL: https://issues.apache.org/jira/browse/HIVE-21290
>             Project: Hive
>          Issue Type: Sub-task
>            Reporter: Zoltan Ivanfi
>            Assignee: Karen Coppage
>            Priority: Major
>
> This sub-task is for implementing the Parquet-specific parts of the following plan:
> h1. Problem
> Historically, the semantics of the TIMESTAMP type in Hive depended on the file format. Timestamps in Avro, Parquet and RCFiles with a binary SerDe had _Instant_ semantics, while timestamps in ORC, textfiles and RCFiles with a text SerDe had _LocalDateTime_ semantics.
> The Hive community wanted to get rid of this inconsistency and have _LocalDateTime_ semantics in Avro, Parquet and RCFiles with a binary SerDe as well. *Hive 3.1 turned off normalization to UTC* to achieve this. While this leads to the desired new semantics, it also leads to incorrect results when new Hive versions read timestamps written by old Hive versions or when old Hive versions or any other component not aware of this change (including legacy Impala and Spark versions) read timestamps written by new Hive versions.
> h1. Solution
> To work around this issue, Hive *should restore the practice of normalizing to UTC* when writing timestamps to Avro, Parquet and RCFiles with a binary SerDe. In itself, this would restore the historical _Instant_ semantics, which is undesirable. In order to achieve the desired _LocalDateTime_ semantics in spite of normalizing to UTC, newer Hive versions should record the session-local local time zone in the file metadata fields serving arbitrary key-value storage purposes.
> When reading back files with this time zone metadata, newer Hive versions (or any other new component aware of this extra metadata) can achieve _LocalDateTime_ semantics by *converting from UTC to the saved time zone (instead of to the local time zone)*. Legacy components that are unaware of the new metadata can read the files without any problem and the timestamps will show the historical Instant behaviour to them.



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