Re: LIKE Query performance - Mailing list pgsql-performance

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@sai.msu.su]
Sent: Wednesday, January 28, 2009 1:27 AM
To: Hari, Balaji
Cc: pgsql-performance@postgresql.org
Subject: Re: [PERFORM] 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@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83