Re: sequential scan performance

Michael,

I'd recommend our contrib/pg_trgm module, which provides
trigram based fuzzy search and return results ordered by similarity
to your query. Read http://www.sai.msu.su/~megera/postgres/gist/pg_trgm/README.pg_trgm
for more details.

Oleg
On Sun, 29 May 2005, Michael Engelhart wrote:

> Hi -
>
> I have a table of about 3 million rows of city "aliases" that I need to query
> using LIKE - for example:
>
> select * from city_alias where city_name like '%FRANCISCO'
>
>
> When I do an EXPLAIN ANALYZE on the above query, the result is:
>
> Seq Scan on city_alias (cost=0.00..59282.31 rows=2 width=42) (actual
> time=73.369..3330.281 rows=407 loops=1)
> Filter: ((name)::text ~~ '%FRANCISCO'::text)
> Total runtime: 3330.524 ms
> (3 rows)
>
>
> this is a query that our system needs to do a LOT. Is there any way to
> improve the performance on this either with changes to our query or by
> configuring the database deployment? We have an index on city_name but when
> using the % operator on the front of the query string postgresql can't use
> the index .
>
> Thanks for any help.
>
> Mike
>
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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