Re: Slow query and using wrong index, how to fix? Probably naive question.. - Mailing list pgsql-general

Leif,

of course. This performs much better (far below one second).

Thanks!
Antonio


Op 22-05-13 11:28, Leif Gunnar Erlandsen schreef:
> You might want to try with UNION and then sort the result of this query.
>
> The index history_lookup_lookupid_creator_index wont be used when you are having an "OR" in your WHERE statement.
>
>  select history.id, history.created, creator, contact, history.type, lookup, lookupid, value
> from history
> where (lookup = 'phone' and lookupid = '672')
> union
>  select history.id, history.created, creator, contact, history.type, lookup, lookupid, value
> from history
> where  creator = '790'
>
> Leif Gunnar Erlandsen
>
>
>
> ________________________________________
> Fra: pgsql-general-owner@postgresql.org [pgsql-general-owner@postgresql.org] på vegne av Antonio Goméz Soto
[antonio.gomez.soto@gmail.com]
> Sendt: 22. mai 2013 10:50
> Til: pgsql-general@postgresql.org
> Emne: [GENERAL] Slow query and using wrong index, how to fix? Probably naive question..
>
> Hi,
>
> I am using postgresql 8.1 (CentOS5). I have the following table:
>
> system # \d history
>                                    Table "public.history"
>   Column  |           Type           |                      Modifiers
> ----------+--------------------------+------------------------------------------------------
>  id       | integer                  | not null default nextval('history_id_seq'::regclass)
>  created  | timestamp with time zone |
>  creator  | integer                  | not null default 1
>  contact  | integer                  | not null default 1
>  type     | character varying        | not null default ''::character varying
>  lookup   | text                     |
>  lookupid | integer                  | not null default 1
>  value    | text                     |
> Indexes:
>     "history_pkey" PRIMARY KEY, btree (id)
>     "history_created_index" btree (created)
>     "history_creator_index" btree (creator)
>     "history_lookup_lookupid_creator_index" btree (lookup, lookupid, creator)
>     "history_lookup_lookupid_index" btree (lookup, lookupid)
> Foreign-key constraints:
>     "history_contact_constraint" FOREIGN KEY (contact) REFERENCES contact(id)
>     "history_creator_constraint" FOREIGN KEY (creator) REFERENCES contact(id)
>
> system # explain select history.id, history.created, creator, contact, history.type, lookup, lookupid, value from
history where (lookup = 'phone' and lookupid = '672') or creator = '790' order by history.creator desc limit 1000; 
>                                                    QUERY PLAN
> ----------------------------------------------------------------------------------------------------------------
>  Limit  (cost=0.00..132041.59 rows=1000 width=58)
>    ->  Index Scan Backward using history_creator_index on history  (cost=0.00..11746815.97 rows=88963 width=58)
>          Filter: (((lookup = 'phone'::text) AND (lookupid = 672)) OR (creator = 790))
> (3 rows)
>
> This table contains 2 million rows, the query takes 800 seconds on SSD HD.
>
> I think - probably naive - the query should use the history_lookup_lookupid_creator_index.
>
> Why doesn't it, and how can I speed up the query?
>
> Thanks,
> Antonio.
>
>
>
>
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