Matthew Jacobs has posted comments on this change.

Change subject: IMPALA-3504: function for current timestamp in UTC, i.e. 

Patch Set 1:

> > As I mentioned in your previous review and/or the JIRA, this
 > needs
 > > to use the query-wide timestamp, i.e. what we do for now().
 > Greetings, Matthew.
 > If you don't mind, I want to propose an idea about this task.
 > Considering three fators of utc_timestamp, local_timestamp and
 > timezone, I believe we have following deductions:
 > utc_timestamp + local_timestamp ? timezone
 > utc_timestamp + timezone ? local_timestamp
 > local_timestamp + timezone ? utc_timestamp
 > PS: So far as I know, the UTC time is essentially the time without
 > any timezone offset. If you don't mind, I want to take the Beijing
 > time as example. Since Beijing timezone is of +8h offset, I can get
 > corresponding UTC time by minusing 8 from current Beijing time. I
 > have done some calculation and calibration using online time
 > service. And this approach works. If you find some mistakes in my
 > approach, please feel free to point them out. Thank you. :)
 > And I have found the following code:
 > query_ctx->__set_now_string(TimestampValue::LocalTime().DebugString());
 > in be/src/service/
 > So please allow me to assume we have local_timestamp of the host
 > where Impala service runs. In this case, we can:
 > 1. directly store the utc_timestamp in the context data structure.
 > Then utc_timestamp() can be accessed like the function now().
 > 2. save the timezone/offset in the context data structure. Then we
 > can use the now() and such timezone/offset to calculate the
 > utc_timestamp.
 > If possbile, would you please tell which solution you prefer?
 > Thank you for reading this long post. :)

Hi Youwei,

Good question, thanks for following up. I think #1 is better because #2 
involves some additional computation on every invocation of utc_timestamp() 
that may get expensive, e.g. "select utc_timestamp() from 
table_with_1billion_rows;". The advantage I see to #2 is if we wanted the 
timezone stored separately for some other reason, but I think right now that 
would be premature.


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Gerrit-MessageType: comment
Gerrit-Change-Id: I5ee6ee192aa469f77c711f27ad324696a42004d1
Gerrit-PatchSet: 1
Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-Owner: Youwei Wang <>
Gerrit-Reviewer: Jim Apple <>
Gerrit-Reviewer: Matthew Jacobs <>
Gerrit-Reviewer: Youwei Wang <>
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