On Thu, Nov 11, 2010 at 10:38 PM, Pavel Stehule <pavel.stehule@xxxxxxxxx> wrote: > 2010/11/12 Jon Nelson <jnelson+pgsql@xxxxxxxxxxx>: >> On Thu, Nov 11, 2010 at 10:26 PM, Pavel Stehule <pavel.stehule@xxxxxxxxx> wrote: >>> Hello >>> >>> look on EXPLAIN ANALYZE command. Probably your statistic are out, and >>> then planner can be confused. EXPLAIN ANALYZE statement show it. >> >> As I noted earlier, I did set statistics to 1000 an re-ran vacuum >> analyze and the plan did not change. > > this change can do nothing. this is default in config. did you use > ALTER TABLE ALTER COLUMN SET STATISTIC = ... ? and ANALYZE No. To be clear: are you saying that changing the value for default_statistics_target, restarting postgresql, and re-running VACUUM ANALYZE does *not* change the statistics for columns created/populated *prior* to the sequence of operations, and that one /must/ use ALTER TABLE ALTER COLUMN SET STATISTICS ... and re-ANALYZE? That does not jive with the documentation, which appears to suggest that setting a new default_statistics_target, restarting postgresql, and then re-ANALYZE'ing a table should be sufficient (provided the columns have not had a statistics target explicitly set). >> What other diagnostics can I provide? This still doesn't answer the >> 40000 row question, though. It seems absurd to me that the planner >> would give up and just use 40000 rows (0.02 percent of the actual >> result). >> > > there can be some not well supported operation, then planner use a > some % from rows without statistic based estimation The strange thing is that the value 40000 keeps popping up in totally diffferent contexts, with different tables, databases, etc... I tried digging through the code and the only thing I found was that numGroups was being set to 40000 but I couldn't see where. -- Jon -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
