Re: Why would this slow the query down so much?

On Tue, 16 Oct 2001 17:58:32 +0100
Stuart Grimshaw wrote:

> On Monday 15 October 2001 16:12 pm, Tom Lane wrote:
> > Stuart Grimshaw <nospam(at)smgsystems(dot)co(dot)uk> writes:
> > > SELECT a.category, b.headline, b.added, c.friendlyname
> > > FROM caturljoin as a
> > > INNER JOIN stories as b ON (a.url = b.source)
> > > INNER JOIN urllist as c ON (a.url = d.urn)
> > > WHERE a.category = 93 ORDER BY b.added DESC LIMIT 1;
> >
> > (I assume "d.urn" is a typo for "c.urn"...)
> >
> > The query plan you show looks pretty reasonable if the planner's row
> > count estimates are in the right ballpark. How many caturljoin rows
> > have category = 93? How many stories rows will match each caturljoin
> > row? How many urllist rows ditto?
>
> There are 194 rows in caturljoin where url = 93, 29806 rows in stories will
> match those 194 rows and only 1 row in urllist will match.
>

If it's convenient, would you try to delete some indices
of the "stories" table? the total number of sorts on the
QUERY PLAN might decrease. However, this trial may be a
vain effort. I can't expect the result of the QUERY PLAN. :-)


The indices: "stories_source",
"stories_unique_story",
and "stories_urn_key"

Regards,
Masaru Sugawara