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Re: Need help - optimizer trouble

From: "ADBAAMD" <adba(dot)amdocs(at)bell(dot)ca>
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "Helge Bahmann" <bahmann(at)math(dot)tu-freiberg(dot)de>, pgsql-novice(at)postgresql(dot)org
Subject: Re: Need help - optimizer trouble
Date: 2001-04-05 15:10:41
Message-ID: 3ACC8AF1.9000508@bell.ca (view raw or flat)
Thread:
Lists: pgsql-novice
Tom Lane wrote:

> "ADBAAMD" <adba(dot)amdocs(at)bell(dot)ca> writes:
> 
>> Tom Lane wrote:
>> 
>>> This behavior is a bit of a hack, which we'll likely reconsider in
>>> future releases, but it does have some redeeming social value too.
> 
>> Perhaps it would be cleaner to have somehing like Oracle's hints?
> 
> Possibly.  Want to enlighten those of us who've never used Oracle about
> how that works?

	You can read (almost) all about it at 
http://technet.oracle.com/doc/server.804/a58246/toc.htm, more to the 
point http://technet.oracle.com/doc/server.804/a58246/optimiz.htm#2250.

	For example:

  SELECT	/*+ STAR */
	doc_id
    FROM
	written_by	AS wb
    JOIN
	author_keyword	AS kw
      ON
	kw.author_id	=  wb.author_id
   WHERE
	kw.keyword	=  'foo'
;


	There is also a /*+ ORDERED */ hint, but I dislike it as it also requires 
query rewriting.  Keep in mind I have an opinion against having to 
rewrite queries for performance reasons, thinking this should be done at 
the optimizer or preferably at the physical level or the 
logical-to-physical mapping.


	Also it does not seems to me very nice to have queries changing behaviour 
from version to version and then back again.



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