On 25 Aug 2003 at 8:44, Stephan Szabo wrote:

> On Mon, 25 Aug 2003, Rhaoni Chiu Pereira wrote:
> > Hi List,
> >
> >      As I said before, I'm not a DBA " yet" , but I'm learning ... and I
> > already have a PostgreSQL running, so I have to ask some help...
> >       I got a SQL as folows :
> ...
> Looking at the explain:
> It's choosing lots of nested loops because it's expecting a small number
> of rows to be returned at each step but in reality there are alot of rows
> so that's may not really be a good choice.
> For example the scan of ftnfco00 is expected to return 295 rows but
> actually returns 9339, and it looks like it's not estimating the number of
> matches between the tables very well either since the real count gets up
> to 240000 in a step where the estimated rows goes to 1.
> What does explain analyze give after set enable_nestloop=off;?

In addition to that if it is getting the stats wrong, does running vacuum 
analyze help? If stats are updated, it should pick up proper plans, right?


Flon's Law:     There is not now, and never will be, a language in      which it is 
least bit difficult to write bad programs.

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TIP 8: explain analyze is your friend

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