Subject: Re: Postgresql  performance
From: Hannu Krosing <hannu@tm.ee>
To: Enix Empreendimentos e =?ISO-8859-1?Q?Constru=E7=F5es?= "Ltda."
	<contato@enix.com.br>
Cc: pgsql-performance@postgresql.org
In-Reply-To: <000701c2e8d8$95637b60$02ada8c0@enix>
References: <000701c2e8d8$95637b60$02ada8c0@enix>
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Date: 14 Mar 2003 00:26:20 +0200

Enix Empreendimentos e Constru=E7=F5es Ltda. kirjutas K, 12.03.2003 kell
22:47:
> Hi everybody.
>=20
> I am a newbie to Postgresql, trying to migrate an application from MSAcce=
ss.
>=20
> I am quite dissapointed with the problems I am facing with some queries
> containing multiple joins.

Postgres currently does *not* optimize join order for explicit joins
(this is currently left as a cludge for users to hand-optimize query
plans).

To get the benefits form optimiser you have to rewrite

FROM TA JOIN TB ON TA.CB=3DTB.CB

to=20

FROM A,B
WHERE TA.CB=3DTB.CB

> I confess it has been hard for someone that is
> not a DBA to figure out which are the problems. Just to ilustrate, I have
> some queries that provide a reasonable query plan (at least from my point=
 of
> view), but that return no result: keep running on and on.

Could you try to explain it in other words (or give an example). I am
not native english speaker and I can read your text in at least 5
different ways ;(

> Is the performance of the mentioned Postgresql version much slower than t=
he
> 7.3.1?

It can be slower. It may also be a little faster in some very specific
cases ;)

--------------
Hannu