Gavin Flower <GavinFlower@xxxxxxxxxxxxxxxxx> writes: > On 11/10/12 01:03, Lars Helge Øverland wrote: >> My question is: Would it be feasible and/or possible to implement >> index only scans in a way that it could take advantage of several, >> single-column indexes? For example, a query spanning columns a, b, c >> could take advantage of 3 single-column indexes put on columns a, b, >> c. > Index only scans do use multiple indexes of single fields where > appropriate. Here the planner determined it only needed to scan 2 of > the 3 relevant single field indexes. But your example isn't an index-only scan ... it's a plain old bitmap scan, and so it does touch the heap. The difficulty with what Lars proposes is that there's no way to scan the different indexes "in sync" --- each one will be ordered according to its own column order. In principle I guess we could read out the index data and do a join using the ctid's, but it's far from clear that such a thing would be worth the trouble. regards, tom lane -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
