On Mon, Jun 1, 2009 at 8:20 PM, Douglas Alan <darkwater42@xxxxxxxxx> wrote: > I'd like to manually alter the statistics for a column, as for the column in > question the statistics are causing Postgres to do the wrong thing for my > purposes. (I.e., a Seq Scan, rather than an Index Scan.) If someone can > tell me how to achieve this, I would quite grateful. > Assuming estimates are off, wouldn't increasing the stats target be a better approach? Then adjust the planner cost constants, in particular seq_page_cost, random_page_cost and effective_cache_size, to prevent a seq scan? Considering you've pulled off the workaround, you must know what you're doing, but I'd be worried about it backfiring in the future. Regards, Isak > Thanks! > |>ouglas > > > P.S. Actually, for this particular problem, just deleting the statistics > would be fine. I've tried doing: > > alter table maindb_astobject alter column survey_id set statistics 0; > > And then analyzing the column, but when "statistics" for a column are set > to 0, Postgres seems to leave the current statistics in place, which is not > the right thing for me at all. I can successfully set "statistics" to 1, > but that turns out to be one statistic too many. > > I've tried settings the statistics via the table "pg_stats", but that turns > out to be a view, and Postgres won't allow to me to alter it. > > Perhaps I can achieve the end by altering the "pg_statistic" table instead, > but that table is more than a bit opaque to me. > > P.P.S The Seq Scan is 2-4 orders of magnitude slower than the Index Scan. > > > > -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
