Thread: statistics question
can statistics help the postgresql performance? if yes how?
"Sidar Lopez Cruz" <sidarlopez@hotmail.com> wrote: > can statistics help the postgresql performance? if yes how? What do you mean with "statistics" ? Anyway the planner use statistics information, collected by postgres statistics collector ( you should turn on it: stats_start_collector = true stats_reset_on_server_start = true stats_command_string = true stats_row_level = true stats_block_level = true ). How: suppose to do a select like this: select * from table_foo where field = X; if the 100 % of rows have field = X is better do a sequenzial scan without jump around use the index, instead if only 0.1 % of the rows have the field = X is better do an index scan ( specially if the table is really huge ). In reality the data partitioning is not 100% or 0.1 % and the planner some time can take wrong decision so you should increase or decrease the cost of index scan or full scan playing with: cpu_tuple_cost cpu_index_tuple_cost cpu_operator_cost I'm sorry to say however that since version 7.X I'm not anymore able to drive correctly the planner, is like the planner consider these values less then before. I hope I was clear enough. Regards Gaetano Mendola