Re: Limit clause not using index

Yves Vindevogel <yves(dot)vindevogel(at)implements(dot)be> writes:
> Can anyone explain me this ?

> rvponp=# explain select * from tblprintjobs order by loginuser,
> desceventdate, desceventtime offset 25 limit 25 ;
> QUERY PLAN
> ------------------------------------------------------------------------
> -----------
> Limit (cost=349860.62..349860.68 rows=25 width=206)
> -> Sort (cost=349860.56..351416.15 rows=622236 width=206)
> Sort Key: loginuser, desceventdate, desceventtime
> -> Seq Scan on tblprintjobs (cost=0.00..25589.36 rows=622236 width=206)
> (4 rows)

Do you have an index matching that sort key? I'd certainly expect the
above to use it if it were there. For the full table case it's not so
clear --- an indexscan isn't always better.

regards, tom lane