Dmitry Teslenko <dteslenko@xxxxxxxxx> wrote: > Seqscan is very slow and I want to avoid it. Subquery is very fast > and i don't know why postgres chooses that plan. > > I know I can set enable_seqscan = off. > Is there other ways to enforce index usage? If you come at it from that angle, you probably won't get the best resolution. PostgreSQL can see the alternative plans, and develops estimated costs of running each. It uses the one that it thinks will be fastest. If it's wrong, there's probably something wrong with the statistics it uses for estimating, or with the costing information. (There are some cases where it's not able to accurately estimate costs even if these are right, but let's check the more common cases first.) Please provide a little more information, like PostgreSQL version, the postgresql.conf contents (excluding comments), OS, hardware, and the EXPLAIN ANALYZE output of the query with and without enable_seqscan = off. Other useful ideas here: http://wiki.postgresql.org/wiki/SlowQueryQuestions -Kevin -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
