Robert Haas <robertmh...@gmail.com> writes: > This issue of detoasting costs comes up a lot, specifically in > reference to @@. I wonder if we shouldn't try to apply some quick and > dirty hack in time for 9.2, like maybe random_page_cost for every row > or every attribute we think will require detoasting. That's obviously > going to be an underestimate in many if not most cases, but it would > probably still be an improvement over assuming that detoasting is > free.
Well, you can't theorize without data, to misquote Sherlock. We'd need to have some stats on which to base "we think this will require detoasting". I guess we could teach ANALYZE to compute and store fractions "percent of entries in this column that are compressed" and "percent that are stored out-of-line", and then hope that those percentages apply to the subset of entries that a given query will visit, and thereby derive a number of operations to multiply by whatever we think the cost-per-detoast-operation is. It's probably all do-able, but it seems way too late to be thinking about this for 9.2. We've already got a ton of new stuff that needs to be polished and tuned... regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers