Re: LIKE Query performance

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



We won't need full text searching capabilities as in documents as the data type is varchar.

Wildspeed will exactly fit our needs.

-----Original Message-----
From: Oleg Bartunov [mailto:oleg@xxxxxxxxxx] 
Sent: Wednesday, January 28, 2009 1:27 AM
To: Hari, Balaji
Cc: pgsql-performance@xxxxxxxxxxxxxx
Subject: Re:  LIKE Query performance

Only wildspeed http://www.sai.msu.su/~megera/wiki/wildspeed
has index support for %text% 
But, it has limitations.

Oleg
On Tue, 27 Jan 2009, Hari, Balaji wrote:

> Hi,
>
> I am relatively new to PostgreSQL(8.1) and facing the following problem.
>
> We have indexes defined on timestamp and description (create index description_idx on event using btree (description varchar_pattern_ops))
>
> EXPLAIN ANALYZE SELECT event_id, category, current_session_number, description, event_type_id, realm_name, root_session_number, severity, source_name, target_key, target_name, timestamp, jdo_version FROM event WHERE description like '%mismatch%' ORDER BY timestamp desc;
>                                                      QUERY PLAN
> ----------------------------------------------------------------------------------------------------------------------
> Sort  (cost=36267.09..36272.73 rows=2256 width=314) (actual time=19255.075..20345.774 rows=647537 loops=1)
>   Sort Key: "timestamp"
>   Sort Method:  external merge  Disk: 194080kB
>   ->  Seq Scan on event  (cost=0.00..36141.44 rows=2256 width=314) (actual time=0.080..1475.041 rows=647537 loops=1)
>         Filter: ((description)::text ~~ '%mismatch%'::text)
> Total runtime: 22547.292 ms
> (6 rows)
>
> But startsWith query use indexes.
>
> EXPLAIN ANALYZE SELECT event_id, category, current_session_number, description, event_type_id, realm_name, root_session_number, severity, source_name, target_key, target_name, timestamp, jdo_version FROM event WHERE description like 'mismatch%' ORDER BY timestamp desc;
>                                                          QUERY PLAN
> -------------------------------------------------------------------------------------------------------------------------------
> Sort  (cost=9.26..9.27 rows=1 width=314) (actual time=0.766..0.766 rows=0 loops=1)
>   Sort Key: "timestamp"
>   Sort Method:  quicksort  Memory: 17kB
>   ->  Index Scan using description_idx on event  (cost=0.00..9.25 rows=1 width=314) (actual time=0.741..0.741 rows=0 loops=1)
>         Index Cond: (((description)::text ~>=~ 'mismatch'::text) AND ((description)::text ~<~ 'mismatci'::text))
>         Filter: ((description)::text ~~ 'mismatch%'::text)
> Total runtime: 0.919 ms
> (7 rows)
>
> Is there any tweaks to force pgsql to use index on description?
>
> Balaji
>
> P.S The event database has 700k records.
>

 	Regards,
 		Oleg
_____________________________________________________________
Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru),
Sternberg Astronomical Institute, Moscow University, Russia
Internet: oleg@xxxxxxxxxx, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83


-- 
Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-performance


[Postgresql General]     [Postgresql PHP]     [PHP Users]     [PHP Home]     [PHP on Windows]     [Kernel Newbies]     [PHP Classes]     [PHP Books]     [PHP Databases]     [Yosemite]

  Powered by Linux