Re: help with query - Mailing list pgsql-performance

Brad,

Thanks, that runs on the same order of magnitude as the subqueries.

DAve
On Thu, 2004-08-19 at 09:38, Brad Bulger wrote:
> You're doing a join except not, is the trouble, looks like. The query is really
> "FROM Tickets main, Links", but when Tickets.id is 17417, you've got no join
> to the Links table. So you end up getting every row in Links for each row in
> Tickets with id = 17417.
>
> I'd think this wants to be two queries or a union:
>
> SELECT distinct main.oid,main.* FROM Tickets main
> WHERE (main.EffectiveId = main.id)
> AND (main.Status != 'deleted')
> AND ( (main.Type = 'ticket') OR (main.Type = 'subticket') )
> AND ( (main.Queue = '9') )
> AND ( (main.id = '17417'))
> union
> SELECT distinct main.oid,main.* FROM Tickets main, Links
> WHERE (main.EffectiveId = main.id)
> AND (main.Status != 'deleted')
> AND ( (main.Type = 'ticket') OR (main.Type = 'subticket') )
> AND ( (main.Queue = '9') )
> AND ( (Links.Type = 'MemberOf') )
> AND ( (Links.LocalTarget = '17417') )
> AND ( (main.id = Links.LocalBase) ) OR (main.id = Links.LocalTarget) )
> ;
>
> or else, yah, a subquery:
>
> [...]
> AND (
>   main.id = '17417'
>   or
>   exists(
>     select true from Links
>     where Type = 'MemberOf' and LocalTarget = '17417'
>      and (LocalBase = main.id or LocalTarget = main.id)
>   )
> )
>
> Those are the only things I can think of to make it work, anyways.
>
> Dave Cramer wrote:
>
> > RT uses a query like:
> >
> > SELECT distinct main.oid,main.* FROM Tickets main
> > WHERE
> > (main.EffectiveId = main.id)
> > AND
> > (main.Status != 'deleted')
> > AND
> >     ( (main.Type = 'ticket') OR (main.Type = 'subticket') )
> > AND
> >     ( (main.Queue = '9') )
> > AND ((
> >         ( (Links.Type = 'MemberOf') AND (Links.LocalTarget = '17417') AND (main.id = Links.LocalBase) )
> >       OR
> >         ( (Links.Type = 'MemberOf') AND (Links.LocalBase = '17417') AND (main.id = Links.LocalTarget) )
> >       or
> >         (main.id = '17417')
> >      )
> >   );
> >
> >
> > which produces a query plan:
> >
> > Nested Loop  (cost=0.00..813.88 rows=1 width=169)
> >    Join Filter: (((("inner"."type")::text = 'MemberOf'::text) OR ("outer".id = 17417)) AND (("inner".localbase =
17417)OR (("inner"."type")::text = 'MemberOf'::text) OR ("outer".id 
> > = 17417)) AND (("outer".id = "inner".localtarget) OR (("inner"."type")::text = 'MemberOf'::text) OR ("outer".id =
17417))AND ((("inner"."type")::text = 'MemberOf'::text) OR ("inner" 
> > .localtarget = 17417) OR ("outer".id = 17417)) AND (("inner".localbase = 17417) OR ("inner".localtarget = 17417) OR
("outer".id= 17417)) AND (("outer".id = "inner".localtarget) OR ( 
> > "inner".localtarget = 17417) OR ("outer".id = 17417)) AND ((("inner"."type")::text = 'MemberOf'::text) OR
("outer".id= "inner".localbase) OR ("outer".id = 17417)) AND (("inner".loca 
> > lbase = 17417) OR ("outer".id = "inner".localbase) OR ("outer".id = 17417)) AND (("outer".id = "inner".localtarget)
OR("outer".id = "inner".localbase) OR ("outer".id = 17417))) 
> >    ->  Index Scan using tickets1 on tickets main  (cost=0.00..657.61 rows=1 width=169)
> >          Index Cond: (queue = 9)
> >          Filter: ((effectiveid = id) AND ((status)::text <> 'deleted'::text) AND ((("type")::text = 'ticket'::text)
OR(("type")::text = 'subticket'::text))) 
> >    ->  Seq Scan on links  (cost=0.00..46.62 rows=1462 width=20)
> >
> > If I rewrite the query as:
> >
> > SELECT main.* FROM Tickets main
> > WHERE
> > (main.EffectiveId = main.id)
> > AND
> > (main.Status != 'deleted')
> > AND
> >     ( (main.Type = 'ticket') OR (main.Type = 'subticket') )
> > AND
> >     ( (main.Queue = '9') )
> > AND (
> >         17417 in (select links.localtarget from links where links.type='MemberOf' and main.id=links.localbase)
> >         or
> >         17417 in ( select links.localbase from links where links.type='MemberOf' and main.id=links.localtarget)
> >       or
> >         main.id = '17417'
> >     )
> >   ;
> >
> > The time for the query goes from 1500ms to 15ms. The two OR clauses
> >
> >         ( (Links.Type = 'MemberOf') AND (Links.LocalTarget = '17417') AND (main.id = Links.LocalBase) )
> >       OR
> >         ( (Links.Type = 'MemberOf') AND (Links.LocalBase = '17417') AND (main.id = Links.LocalTarget) )
> >
> > don't contribute to the result set in this particular dataset, which is why the speed increases so dramatically.
> >
> > Is there a way to rewrite the top query to get the same results? I have already talked to Best Practical,
> > and subqueries are not easily embraced.
> >
> > Dave
>
--
Dave Cramer
519 939 0336
ICQ # 14675561