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Re: combined indexes with Gist - planner issues?

From: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
To: Hans-Juergen Schoenig -- PostgreSQL <postgres(at)cybertec(dot)at>
Cc: Martijn van Oosterhout <kleptog(at)svana(dot)org>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Zoltan Boszormenyi <zb(at)cybertec(dot)at>
Subject: Re: combined indexes with Gist - planner issues?
Date: 2009-08-31 15:27:18
Message-ID: 4A9BEBD6.60407@enterprisedb.com (view raw or flat)
Thread:
Lists: pgsql-hackers
Hans-Juergen Schoenig -- PostgreSQL wrote:
> my knowledge of how gist works internally is not too extensive. any
> "kickstart" idea would be appreciated.

If there's not too many of those common words, you can create a simple
partial b-tree index for each, and handle the less common words with the
gist index you have (you can drop the display_price column from the index).

Another idea:

Create a table containing one row for each word in each product:

CREATE TABLE t_product_word (id bigint, word text, display_price
numeric(10,4));

with triggers to keep it up-to-date. You can then create a regular two
column b-tree index on that:

CREATE INDEX idx_word_price ON t_product_word (word, display_price);

And query with:

SELECT p.art_number, p.title
   FROM t_product p INNER JOIN t_product_word pw ON p.id = pw.id
   WHERE pw.word = 'harddisk'
ORDER BY pw.display_price DESC LIMIT 10;

The t_product_word table will be huge, but with a few gigabytes of data
it should still be manageable.

-- 
  Heikki Linnakangas
  EnterpriseDB   http://www.enterprisedb.com

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Subject: Re: combined indexes with Gist - planner issues?
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