[jira] [Work logged] (HIVE-26507) Do not allow hive to iceberg migration if source table contains CHAR or VARCHAR columns

["ASF GitHub Bot (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HIVE-26507?focusedWorklogId=805523&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-805523 ]

ASF GitHub Bot logged work on HIVE-26507:
-----------------------------------------

                Author: ASF GitHub Bot
            Created on: 01/Sep/22 13:11
            Start Date: 01/Sep/22 13:11
    Worklog Time Spent: 10m 
      Work Description: lcspinter opened a new pull request, #3570:
URL: https://github.com/apache/hive/pull/3570

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   ### What changes were proposed in this pull request?
   Raise exception when trying to convert hive table to iceberg if the hive table contains CHAR or VARCHAR columns.
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   ### Why are the changes needed?
   Previously CHAR and VARCHAR columns were mapped to STRING columns on the iceberg side since iceberg doesn't have support for those. 
   CHAR and VARCHAR types are fixed-length meaning that the values can be shorter than the specified length, and the remaining characters are padded with spaces. These spaces are trimmed during comparison.
   
   When a table is migrated to iceberg the CHAR columns are read as a STRING on the iceberg side, therefore the whole content of the record is considered important. When running a filter against these columns we would need to add the whole content of the record, including white spaces. This can cause confusion since the same query run on a hive and iceberg table can return different results.
   
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   ### Does this PR introduce _any_ user-facing change?
   When running the iceberg migration command, an exception is raised if the source table contains CHAR or VARCHAR columns. As a workaround, the dataset of the source table should be converted to string.
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   ### How was this patch tested?
   Unit test
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Issue Time Tracking
-------------------

            Worklog Id:     (was: 805523)
    Remaining Estimate: 0h
            Time Spent: 10m

> Do not allow hive to iceberg migration if source table contains CHAR or VARCHAR columns
> ---------------------------------------------------------------------------------------
>
>                 Key: HIVE-26507
>                 URL: https://issues.apache.org/jira/browse/HIVE-26507
>             Project: Hive
>          Issue Type: Bug
>            Reporter: Rajesh Balamohan
>            Assignee: László Pintér
>            Priority: Major
>              Labels: iceberg
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> "alter table" statements can be used for generating iceberg metadata information (i.e for converting external tables  -> iceberg tables).
> As part of this process, it also converts certain datatypes to iceberg compatible types (e.g char -> string). "iceberg.mr.schema.auto.conversion" enables this conversion.
> This could cause certain issues at runtime. Here is an example
> {noformat}
> Before conversion:
> ==================
> -- external table
> select count(*) from customer_demographics where cd_gender = 'F' and cd_marital_status = 'U' and cd_education_status = '2 yr Degree';
> 27440
> after conversion:
> =================
> -- iceberg table
> select count(*) from customer_demographics where cd_gender = 'F' and cd_marital_status = 'U' and cd_education_status = '2 yr Degree';
> 0
> select count(*) from customer_demographics where cd_gender = 'F' and cd_marital_status = 'U' and trim(cd_education_status) = '2 yr Degree';
> 27440
>  {noformat}
>  



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