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Re: tsearch2 poor performance

From: Oleg Bartunov <oleg(at)sai(dot)msu(dot)su>
To: Kris Kiger <kris(at)musicrebellion(dot)com>
Cc: pgsql-admin(at)postgresql(dot)org
Subject: Re: tsearch2 poor performance
Date: 2004-09-24 17:20:36
Message-ID: Pine.GSO.4.58.0409242114270.14980@ra.sai.msu.su (view raw or flat)
Thread:
Lists: pgsql-admin
Kris,

could you post 'explain analyze' output ?
Also, could you disable index usage (set enable_indexscan=off)
and rerun search using tsearch2 ?

also, could you run 'stat' function to see frequency distribution
of words. See http://www.sai.msu.su/~megera/oddmuse/index.cgi/Tsearch_V2_Notes
for details.

Oleg
On Fri, 24 Sep 2004, Kris Kiger wrote:

> Hi all.  I am doing some work with tsearch2 and am not sure what to
> expect out of it, performance wise.  Here is my setup:
>
>                           Table "public.product"
>    Column    |   Type   |                    Modifiers
> -------------+----------+-------------------------------------------------
>  description | text     |
>  product_id  | integer  | default nextval('product_product_id_seq'::text)
>  vector      | tsvector |
> Indexes:
>     "vector_idx" gist (vector)
> Triggers:
>     tsvectorupdate BEFORE INSERT OR UPDATE ON product FOR EACH ROW EXECUTE PROCEDURE tsearch2('vector', 'description')
>
> This table has 3,000,000 rows in it.  Each description field has roughly 50 characters.  There are fewer than ten thousand distinct words in my 3,000,000 rows.  The vector was filled using the description fields values.  I ran a vacuum full analyze before executing any of my queries.
>
> Here are a couple of tests I performed using the tsearch index and like;
>
> search_test=# select count(*) from product where vector @@ to_tsquery('oil');
>  count
> --------
>  226357
> (1 row)
>
> Time: 191056.230 ms
>
> search_test=# select count(*) from product where vector @@ to_tsquery('hydrogen');
>  count
> --------
>  226868
> (1 row)
>
> Time: 306411.957 ms
>
> search_test=# select count(*) from product where description like '% oil %';
>  count
> --------
>  226357
> (1 row)
>
> Time: 38426.851 ms
>
> search_test=# select count(*) from product where description like '% hydrogen %';
>  count
> --------
>  226868
> (1 row)
>
> Time: 38265.421 ms
>
>
> Both of the likes are using a sequential scan and both of the tsearch queries use the gist index.  Did I miss a configuration parameter, are these queries incorrectly using tsearch2,or is this tsearch2's average performance?  Thanks in advance for the input!
>
> Kris
>
>
>
>
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	Regards,
		Oleg
_____________________________________________________________
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: oleg(at)sai(dot)msu(dot)su, http://www.sai.msu.su/~megera/
phone: +007(095)939-16-83, +007(095)939-23-83

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