On 2011-06-20 17:38, Sushant Sinha wrote:
I have a tsvector column docvector and a gin index on it
docmeta1_docvector_idx
I have a simple query "select * from docmeta1 where docvector @@
plainto_tsquery('english', 'free');"
I find that the planner chooses a sequential scan of the table even when
the index performs orders of magnitude. I set random_page_cost = 1.0 for
the database to favor index use. However, I still see that the cost
estimate for sequential scan of the entire table (23000) is cheaper than
the cost of using the index (33000). The time taken for sequential
access is 5200 ms and for index usage is only 85 ms.
The cost-estimation code for gin-indices are not good in 9.0, this has
hugely been improved in 9.1
http://git.postgresql.org/gitweb?p=postgresql.git&a=search&h=HEAD&st=commit&s=gincost
I think the individual patches apply quite cleanly to 9.0 as far
as I remember.
--
Jesper
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