Hi. I'm interested in understanding the differences between CLUSTERing a table and making a dedicated one. We have a table with about 1 million records. On a given day, only about 1% of them are of interest. That 1% changes every day (it's WHERE active_date = today), and so we index and cluster on it. Even so, the planner shows a very large cost for the Index Scan: about 3500. If I instead do a SELECT INTO temp_table FROM big_table WHERE active_date = today, and then do SELECT * FROM temp_table, I get a planned cost of 65. Yet, the actual time for both queries is almost identical. Questions: 1. Why is there such a discrepancy between the planner's estimate and the actual cost? 2. In a case like this, will I in general see a performance gain by doing a daily SELECT INTO and then querying from that table? My ad hoc test doesn't indicate I would (despite the planner's prediction), and I'd rather avoid this if it won't help. 3. In general, does CLUSTER provide all the performance benefits of a dedicated table? If it doesn't, what does it lack? Thank you. -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
