Re: Tuning Query w/database link
- From: Michael Thomas <mhthomas@xxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Fri, 6 Aug 2004 15:16:31 -0700 (PDT)
Hi,
--- "Hostetter, Jay M"
<JHostetter@xxxxxxxxxxxxxxxxxxxx> wrote:
> I am trying to help a developer tune a query that
> uses a database link.
> For testing purposes, I've broken the query down to
> the simple query
> shown below. TEST_VIEW is a remote view that joins
> three tables, which
> results in approximately 1 million rows. The query
> that Oracle passes
> to the remote database never has a predicate - it is
> always 'select *
> from test_view'. I have tried various hints, but I
...
Have you tried subqueries and the PUSH_SUBQ (or its
converse) hint? The idea being to either get/push the
least data across the link from either side. E.g.
One simple example (push a few local rows) is:
SELECT /* PUSH_SUBQ */ r.col1, r.col2, r.col3
FROM tableA@remote_link r
WHERE (r.col1, r.col2) in (
SELECT l.col4, l.col5
FROM local_tableB l
WHERE l.col6 = 'ABC' )
;
(PS: Watch out for possible NULLs)
I have used this technique many times with success.
Regards,
Mike Thomas
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