Thom Brown <thom@xxxxxxxxx> writes: > On 18 October 2012 17:44, Tom Lane <tgl@xxxxxxxxxxxxx> wrote: >> Thom Brown <thom@xxxxxxxxx> writes: >>> And as a side note, how come it's impossible to get the planner to use >>> an index-only scan to satisfy the query (disabling sequential and >>> regular index scans)? >> Implementation restriction - we don't yet have a way to match index-only >> scans to expressions. > Ah, I suspected it might be, but couldn't find notes on what scenarios > it's yet to be able to work in. Thanks. I forgot to mention that there is a klugy workaround: add the required variable(s) as extra index columns. That is, create index i on t (foo(x), x); The planner isn't terribly bright about this, but it will use that index for a query that only requires foo(x), and it won't re-evaluate foo() (though I think it will cost the plan on the assumption it does :-(). regards, tom lane -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
