when to update pg_statistic relation? is it when inserting a new tuple of
any user's relations? and the relation pg_stats at document 8.4 chapter
44.55.pg_stats hasn't been used anymore ?
another question is:
I noticed when i send the sql :"select catcode from pois goup by catcode",
the function :double estimate_num_groups(PlannerInfo *root, List
*groupExprs, double input_rows) uses pg_statistic.staattnum to set
Agg.numGroups, then if the pg_statistic.staattnum is incorrect ,does
postgresql still use this infomation to set Agg.numGroups ?