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https://issues.apache.org/jira/browse/HIVE-25576?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17756851#comment-17756851
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Stamatis Zampetakis commented on HIVE-25576:
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I added an entry about the hive.datetime.formatter property in the wiki:
https://cwiki.apache.org/confluence/display/Hive/Configuration+Properties#ConfigurationProperties-Datetime
I updated the from_unixtime and unix_timestamp entries in the wiki:
https://cwiki.apache.org/confluence/display/hive/languagemanual+udf#LanguageManualUDF-DateFunctions
> Configurable datetime formatter for unix_timestamp, from_unixtime
> -----------------------------------------------------------------
>
> Key: HIVE-25576
> URL: https://issues.apache.org/jira/browse/HIVE-25576
> Project: Hive
> Issue Type: Improvement
> Affects Versions: 3.1.0, 3.0.0, 3.1.1, 3.1.2, 4.0.0-beta-1
> Reporter: Ashish Sharma
> Assignee: Stamatis Zampetakis
> Priority: Major
> Labels: pull-request-available
> Fix For: 4.0.0
>
> Time Spent: 3h
> Remaining Estimate: 0h
>
> HIVE-25403, HIVE-25458 switched the internal implementation of datetime
> formatter for unix_timestamp and from_unixtime from
> {{java.text.SimpleDateFormat}} to {{java.time.format.DateTimeFormatter}} in
> order fix some bugs and inconsistencies when the aforementioned functions are
> combined with other UDFs that have already migrated to use the new modern
> java.time package.
> The two Java formatters present differences in their behavior leading to
> different query results. The supported patterns, between the two formatters,
> are also different something that makes existing queries crash at runtime
> (after upgrade). Adapting to the new behavior of DateTimeFormatter is a
> challenging and time-consuming task for end users especially due to the
> widespread use of the afforementioned unixtime functions.
> Although DateTimeFormatter is a clear improvement over SimpleDateFormat some
> users still want to retain the old behavior for compatibility reasons thus
> introducing a property is necessary for facilitating migration.
> The goal of this ticket is to introduce a new property namely
> {{hive.datetime.formatter}} to control the formatter used by unix_timestamp
> and from_unixtime. By default the new {{DateTimeFormatter}} is used while the
> use of {{SimpleDateFormat}} is discouraged. Eventually, {{SimpleDateFormat}}
> will cease to exist.
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