Thread: NOW vs CURRENT_DATE

Hello every body,

I just discover a big not only big huge difference between NOW() and
CURRENT_DATE.

Did you already know about it and do you know why ?

DELETE FROM blacklist where bl_date < (NOW() - interval '2 DAY');
on 6 000 000 of records
699 ms

DELETE FROM blacklist where bl_date < (CURRENT_DATE - interval '2 DAY');
on 6 000 000 of records

0.065 ms

tx

david

> I just discover a big not only big huge difference between NOW() and
> CURRENT_DATE.
>
> Did you already know about it and do you know why ?
>
> DELETE FROM blacklist where bl_date < (NOW() - interval '2 DAY');
> on 6 000 000 of records
> 699 ms
>
> DELETE FROM blacklist where bl_date < (CURRENT_DATE - interval '2 DAY');
> on 6 000 000 of records

Is this a one-off run after each other (e.g. with a ROLLBACK in
between)? If so I suspect the difference is due to caching and if you
re-run the NOW() version it would also be fast.

Also, NOW() is equivalent to CURRENT_TIMESTAMP() rather than
CURRENT_DATE(). Perhaps the date vs. timestamp has some implication of
how they query is planned.

--
/ Peter Schuller

PGP userID: 0xE9758B7D or 'Peter Schuller <peter.schuller@infidyne.com>'
Key retrieval: Send an E-Mail to getpgpkey@scode.org
E-Mail: peter.schuller@infidyne.com Web: http://www.scode.org

Hi,

dforum wrote:
> Hello every body,
>
> I just discover a big not only big huge difference between NOW() and
> CURRENT_DATE.
>
> Did you already know about it and do you know why ?
>
> DELETE FROM blacklist where bl_date < (NOW() - interval '2 DAY');
> on 6 000 000 of records
> 699 ms
>
> DELETE FROM blacklist where bl_date < (CURRENT_DATE - interval '2 DAY');
> on 6 000 000 of records

Try that with a timestamp - column and use now() and current_timestamp
with a long running query and then compare min(column) max(column) in
both cases :-)

Regards
Tino