On 06/20/2011 10:55 AM, adrien ducos wrote:
I think this should at least be writen in this documentation: http://www.postgresql.org/docs/9.0/static/indexes-partial.html as a known limitation to avoid people spending hours of search for why is the application becoming slow.
It's documented in the "Notes" section of http://www.postgresql.org/docs/9.0/static/sql-prepare.html because it's not specific to partial indexes. Prepared statements are very risky when you run them against queries with a very skewed distribution, like your case where 99% of the values for a column are the same. They help to prevent SQL injection and can reduce parsing/planning overhead, but prepared statements can have terrible performance in some unfortunately common situations. Just recently I had one clients end up switching to another ORM specifically because they couldn't get the one they started with to stop using prepared statements, and those gave them terrible query plans.
-- Greg Smith 2ndQuadrant US greg@xxxxxxxxxxxxxxx Baltimore, MD PostgreSQL Training, Services, and 24x7 Support www.2ndQuadrant.us "PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books -- Sent via pgsql-admin mailing list (pgsql-admin@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-admin
