| From: | Jeff Janes <jeff(dot)janes(at)gmail(dot)com> |
|---|---|
| To: | Daniel Tahara <daniel(dot)tahara(at)yale(dot)edu> |
| Cc: | "pgsql-general(at)postgresql(dot)org" <pgsql-general(at)postgresql(dot)org> |
| Subject: | Re: What does \timing measure? |
| Date: | 2013-09-24 22:07:23 |
| Message-ID: | CAMkU=1zrDrqDzuANKR-PH2kNweSdYt5t7y6uRtoVccXjuZu9+Q@mail.gmail.com |
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| Lists: | pgsql-general |
On Tue, Sep 24, 2013 at 1:13 PM, Daniel Tahara <daniel(dot)tahara(at)yale(dot)edu>wrote:
> I am attempting to benchmark a number of queries over a 15GB dataset with
> ~ 10mil records. When I run linux time on the query execution (single
> column projection), it returns 1 minute, but the \timing command returns
> only 15 seconds?
>
Can you show exactly how you are executing those?
> Can someone explain the difference? 1 minute is consistent with reading
> the 15gb from disk at 250mb/s (I have SSDs), but is \timing supposed to
> include that cost? Or simply the computation time plus the time to return
> results.
>
Probably much of your data is cached in RAM so doesn't have be read from
disk anyway. To the extent it does need to be read from disk, that time
will be included.
psql's \timing doesn't include the time it takes for psql to format and
print the results to the screen (or whereever the output of psql is sent).
Cheers,
Jeff
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