Re: LIKE Query performance

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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@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




	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

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