biuro@xxxxxxxxxxxxxxxxx writes: > [slow:] > OPEN cursor1 FOR SELECT * FROM alias WHERE mask>=alias_out > ORDER BY mask; > [fast:] > OPEN cursor1 FOR SELECT * FROM alias WHERE mask>=alias_out > ORDER BY mask LIMIT 100; The difference is that in the first case the planner has to assume you intend to fetch all the rows with mask>=something (and I'll bet the something is a plpgsql variable, so the planner can't even see its value). In this case a sort-based plan looks like a winner. In the second case, since you only need to fetch 100 rows, it's clearly best to scan the index beginning at mask = alias_out. > Can somebody clarify what is wrong with my example? I need select > without LIMIT 100 part. Why? You should always tell the SQL engine what it is that you really want --- leaving it in the dark about your intentions is a good way to destroy performance, as you are finding out. If I were you I would get rid of the row-counting inside the loop entirely, and use the "LIMIT n" clause to handle that. regards, tom lane
