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Re: LIKE Query performance

From: Oleg Bartunov <oleg(at)sai(dot)msu(dot)su>
To: "Hari, Balaji" <Balaji_Hari(at)bmc(dot)com>
Cc: "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: LIKE Query performance
Date: 2009-01-29 19:06:13
Message-ID: Pine.LNX.4.64.0901292205510.9554@sn.sai.msu.ru (view raw or flat)
Thread:
Lists: pgsql-performance
On Thu, 29 Jan 2009, Hari, Balaji wrote:

> Is there a patch to make Wildspeed work with postgresql version 8.3.1?

unfortunately, no.

>
> P.S
> My bad, the version number was incorrect in my previous mail.
> -----Original Message-----
> From: Oleg Bartunov [mailto:oleg(at)sai(dot)msu(dot)su]
> Sent: Wednesday, January 28, 2009 1:27 AM
> To: Hari, Balaji
> Cc: pgsql-performance(at)postgresql(dot)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(at)sai(dot)msu(dot)su, http://www.sai.msu.su/~megera/
> phone: +007(495)939-16-83, +007(495)939-23-83
>
>
>

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

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