Re: about explain analyze

On Fri, 28 Nov 2003, Tom Lane wrote:

> "Marc G. Fournier" <scrappy@postgresql.org> writes:
> > did you happen to take a look at the other set of queries I sent you, that
> > were showing 39k and 41k explain results?
>
> You mean this one?

Yup ...

> > time psql -c "explain analyze select max(intag) from ndict3" 186_archives
>                                                          QUERY PLAN
>
----------------------------------------------------------------------------------------------------------------------------
>  Aggregate  (cost=40168.96..40168.96 rows=1 width=4) (actual time=48953.823..48953.827 rows=1 loops=1)
>    ->  Seq Scan on ndict3  (cost=0.00..34560.57 rows=2243357 width=4) (actual time=4.903..-666785.605 rows=3516680
loops=1)
>  Total runtime: 48982.514 ms
> (3 rows)
>
> 0.000u 0.005s 0:49.06 0.0%      0+0k 0+0io 0pf+0w
> > time psql -c "select max(intag) from ndict3" 186_archives
>     max
> ------------
>  2147418368
> (1 row)
>
> 0.000u 0.005s 0:03.06 0.0%      0+0k 0+0io 0pf+0w
>
> This looks like 46 seconds of overhead for 3516680 rows, or still right
> about 13 microseconds per row, so that's consistent.  The negative
> "actual time" measurement for the Seq Scan row seems pretty broken
> though :-(.
>
> Now that I recall, didn't you complain of something similar with a beta?

Yup ... and I bet its not reproducible yet again, is it? :)  That would
make for twice though, with v7.4, that I've come up with - results :)

----
Marc G. Fournier           Hub.Org Networking Services (http://www.hub.org)
Email: scrappy@hub.org           Yahoo!: yscrappy              ICQ: 7615664