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Re: hints in Postgres?

From: Bruno Wolff III <bruno(at)wolff(dot)to>
To: sandra ruiz <mileruiz(at)hotmail(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: hints in Postgres?
Date: 2003-12-11 20:27:55
Message-ID: 20031211202755.GB9844@wolff.to (view raw or flat)
Thread:
Lists: pgsql-performance
On Thu, Dec 11, 2003 at 11:00:19 -0500,
  sandra ruiz <mileruiz(at)hotmail(dot)com> wrote:
> Hi list,
> 
> I need to know if there is anything like hints of Oracle in 
> Postgres..otherwise..I wish to find a way to force a query plan to use the 
> indexes or tell the optimizer things like "optimize based in statistics", 
> "I want to define the order of the a join" , "optimize based on a execution 
> plan that I consider the best" ...

There are a few things you can do.

You can explicitly fix the join order using INNER JOIN (in 7.4 you have to set
a GUC variable for this to force join order).

You can disable specific plan types (though sequential just becomes very
expensive as sometimes there is no other way to do things).

You can set tuning values to properly express the relative cost of things
like CPU time, sequential disk reads and random disk reads.

These are done by setting GUC variables either in the postgres config
file or using SET commands. They are per backend so some queries can
be done using one set of values while others going on at the same time
use different values.

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