Robert Haas wrote: > experience, most bad plans are caused by bad selectivity estimates, > and the #1 source of bad selectivity estimates is selectivity > estimates for unknown expressions.
ISTM unknown expressions should be modeled as a range of values rather than one single arbitrary value. For example, rather than just guessing 1000 rows, if an unknown expression picked a wide range (say, 100 - 10000 rows; or maybe even 1 - table_size), the planner could choose a plan which wouldn't be pathologically slow regardless of if the guess was too low or too high. For that matter, it seems if all estimates used a range rather than a single value, ISTM less in general we would product less fragile plans. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
