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https://issues.apache.org/jira/browse/HIVE-12192?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16426368#comment-16426368
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Jesus Camacho Rodriguez commented on HIVE-12192:
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[~haozhun], thanks for the experiments. I think you added a new dimension to
the problem :) I was referring to servers in multiple time zones, it would be
great if you could validate whether my statements were correct in that case.
Client and server in different time zones probably causes other different
issues (that this patch would also address). I see why you mention that they
behave as instant, but it is rather confusing. The instant is created taking as
a reference the client's time zone. However, when we read it back, the instant
is not shown taking the client's time zone as a reference, but rather the
server's time zone? (I am looking at experiment 2)
The reason why we added timestamp with local tz before working on this
timestamp issue is that if user wants to obtain instant semantics, they will
still be able to do it via timestamp with local tz.
> Hive should carry out timestamp computations in UTC
> ---------------------------------------------------
>
> Key: HIVE-12192
> URL: https://issues.apache.org/jira/browse/HIVE-12192
> Project: Hive
> Issue Type: Sub-task
> Components: Hive
> Reporter: Ryan Blue
> Assignee: Jesus Camacho Rodriguez
> Priority: Major
> Labels: timestamp
> Attachments: HIVE-12192.patch
>
>
> Hive currently uses the "local" time of a java.sql.Timestamp to represent the
> SQL data type TIMESTAMP WITHOUT TIME ZONE. The purpose is to be able to use
> {{Timestamp#getYear()}} and similar methods to implement SQL functions like
> {{year}}.
> When the SQL session's time zone is a DST zone, such as America/Los_Angeles
> that alternates between PST and PDT, there are times that cannot be
> represented because the effective zone skips them.
> {code}
> hive> select TIMESTAMP '2015-03-08 02:10:00.101';
> 2015-03-08 03:10:00.101
> {code}
> Using UTC instead of the SQL session time zone as the underlying zone for a
> java.sql.Timestamp avoids this bug, while still returning correct values for
> {{getYear}} etc. Using UTC as the convenience representation (timestamp
> without time zone has no real zone) would make timestamp calculations more
> consistent and avoid similar problems in the future.
> Notably, this would break the {{unix_timestamp}} UDF that specifies the
> result is with respect to ["the default timezone and default
> locale"|https://cwiki.apache.org/confluence/display/Hive/LanguageManual+UDF#LanguageManualUDF-DateFunctions].
> That function would need to be updated to use the
> {{System.getProperty("user.timezone")}} zone.
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