Robert Haas <robertmhaas@xxxxxxxxx> wrote: > Wow. That's fascinating, and if you don't mind, I might mention > this potential problem in a future talk at some point. I don't mind at all. > For example, in your case, it would be sufficient to estimate the > amount of data that a given query is going to grovel through and > then applying some heuristic to choose values for random_page_cost > and seq_page_cost based on the ratio of that value to, I don't > know, effective_cache_size. That's where my day-dreams on the topic have been starting. > Unfortunately, to know how much data we're going to grovel > through, we need to know the plan; and to decide on the right > plan, we need to know how much data we're going to grovel through. And that's where they've been ending. The only half-sane answer I've thought of is to apply a different cost to full-table or full-index scans based on the ratio with effective cache size. A higher cost for such scans is something which I've already postulated might be worthwhile for SSI, because of the increased risk of rw-conflicts which could ultimately contribute to serialization failures -- to attempt to model, at least in some crude way, the costs associated with transaction retry. -Kevin -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
