On Fri, Aug 27, 2010 at 1:57 PM, Scott Marlowe <scott.marlowe@xxxxxxxxx> wrote: > On Thu, Aug 26, 2010 at 4:32 AM, Willy-Bas Loos <willybas@xxxxxxxxx> wrote: >> Hi, >> >> I have a colleague that is convinced that the website is faster if >> enable_seqscan is turned OFF. >> I'm convinced of the opposite (better to leave it ON), but i would like to >> show it, prove it to him. > > Stop, you're both doing it wrong. The issue isn't whether or not > turning off seq scans will make a few things faster here and there, > it's why is the query planner choosing sequential scans when it should > be choosing index scans. > > So, what are your non-default settings in postgresql.conf? > Have you increased effective_cache_size yet? > Lowered random_page_cost? > Raised default stats target and re-analyzed? > > Have you been looking at the problem queries with explain analyze? > What does it have to say about the planners choices? [a bit behind on my email] This was exactly my thought on first reading this post. If the indexes are faster and PG thinks they are slower, it's a good bet that there are some parameters that need tuning. Specifically, effective_cache_size may be too low, and random_page_cost and seq_page_cost are almost certainly too high. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise Postgres Company -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
