Yes, fetching a RID list from an index scan, sorting 'em and then
fetching from the table would be a very appreciable speedup for many
queries. I would imagine that all the commercial engines do this (db2
calls it a sorted RID-list-fetch) .. and this has in fact been
discussed on -hackers before.
One issue for this is that there could be a slip between the cup and
the lip .. ie., between the fetch from the index, the sort, and the
fetch from the table a vaccuum could have taken place rendering TIDs
invalid. This should however not be a show-stopper .. surely all
that's needed is a lock against vaccuuming in the presence of a
tid-list-fetch.
--
Pip-pip
Sailesh
http://www.cs.berkeley.edu/~sailesh