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
> > 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:
> in be/src/service/impala-server.cc:841.
> 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
> If possbile, would you please tell which solution you prefer?
> Thank you for reading this long post. :)
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-Owner: Youwei Wang <youwei.a.w...@intel.com>
Gerrit-Reviewer: Jim Apple <jbap...@cloudera.com>
Gerrit-Reviewer: Matthew Jacobs <m...@cloudera.com>
Gerrit-Reviewer: Youwei Wang <youwei.a.w...@intel.com>