On Wed, Aug 26, 2009 at 6:29 PM, Tom Lane<tgl@xxxxxxxxxxxxx> wrote: > gael@xxxxxxxxxxxxxxxx (=?iso-8859-1?Q?Ga=EBl?= Le Mignot) writes: >> So it seems it was quite wrong about estimated matching rows (192 predicted, 10222 reals). > > Yup. What's even more interesting is that it seems the real win would > have been to use just the 'claude & duviau' condition (which apparently > matched only 14 rows). 8.3 had no hope whatever of understanding that, > it just got lucky. 8.4 should have figured it out, I'm thinking. > Does it help if you increase the statistics target for fulltext_tsv? > (Don't forget to re-ANALYZE after doing so.) It could be interesting to run the query without the condition (keywords_tsv @@ '''assassinat'''::tsquery) to see the estimate of (fulltext_tsv @@ '''claud'' & ''duviau'''::tsquery) in 8.4. Btw, what Tom means by increasing the statistics is executing the following queries: ALTER TABLE libeindex ALTER COLUMN fulltext_tsv SET STATISTICS 500; ANALYZE; run your query with EXPLAIN ANALYZE; ALTER TABLE libeindex ALTER COLUMN fulltext_tsv SET STATISTICS 1000; ANALYZE; run your query with EXPLAIN ANALYZE; ALTER TABLE libeindex ALTER COLUMN fulltext_tsv SET STATISTICS 5000; ANALYZE; run your query with EXPLAIN ANALYZE; to see if it improves the estimates. -- Guillaume -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
