Re: Need help - optimizer trouble

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.

--
_
/ \ Leandro Guimarães Faria Corsetti Dutra +55 (11) 3040 8913
\ / Amdocs at Bell Canada +1 (514) 786 87 47
X Support Center, São Paulo, Brazil mailto:adbaamd(at)bell(dot)ca
/ \ http://terravista.pt./Enseada/1989/ mailto:leandrod(at)amdocs(dot)com