Re: REPOST: Nested loops row estimates always too high

On Thu, 2007-09-20 at 11:02 -0400, Carlo Stonebanks wrote:
> (SORRY FOR THE REPOST, I DON'T SEE MY ORIGINAL QUESTION OR ANY ANSWERS HERE)
>
> I am noticing that my queries are spending a lot of time in nested loops.
> The table/index row estimates are not bad, but the nested loops can be off
> by a factor of 50. In any case, they are always too high.
>
> Are the over-estimations below significant, and if so, is this an indication
> of a general configuration problem?
Sounds much like the issue I was seeing as well.

>
> Unique (cost=67605.91..67653.18 rows=4727 width=16) (actual
> time=8634.618..8637.918 rows=907 loops=1)

You can to rewrite the queries to individual queries to see it if helps.

In my case, I was doing

select a.a,b.b,c.c from
(select a from x where) a <--- Put as a SRF
left join (
select b from y where ) b <--- Put as a SRF
on a.a = b.a