> It seems related to this thread? : > https://www.postgresql.org/message-id/flat/5037A9C5.4030701%40optionshouse.com#5037a9c5.4030...@optionshouse.com > > And this wiki page : https://wiki.postgresql.org/wiki/Loose_indexscan
Yep. Now i can see 2 use cases for this feature: 1. DISTINCT queries. 2. Effectively scanning multicolumn index if first column is omitted and has low cardinality > Not an answer to your question, but generally +1 for working on this > area. I did some early proto-hacking a while ago, which I haven't had > time to get back to yet: > > https://www.postgresql.org/message-id/flat/CADLWmXWALK8NPZqdnRQiPnrzAnic7NxYKynrkzO_vxYr8enWww%40mail.gmail.com > > <https://www.postgresql.org/message-id/flat/CADLWmXWALK8NPZqdnRQiPnrzAnic7NxYKynrkzO_vxYr8enWww%40mail.gmail.com> > > That was based on the idea that a DISTINCT scan using a btree index to > skip ahead is always going to be using the leading N columns and > always going to be covered by the index, so I might as well teach > Index Only Scan how to do it directly rather than making a new node to > sit on top. As you can see in that thread I did start thinking about > using a new node to sit on top and behave a bit like a nested loop for > the more advanced feature of an Index Skip Scan (trying every value of > (a) where you had an index on (a, b, c) but had a WHERE clause qual on > (b, c)), but the only feedback I had so far was from Robert Haas who > thought that too should probably be pushed into the index scan. Thank you for information, i will look at this thread. > FWIW I'd vote for 'skip' rather than 'loose' as a term to use in this > family of related features (DISTINCT being the easiest to build). It > seems more descriptive than the MySQL term. (DB2 added this a little > while ago and went with 'index jump scan', suggesting that we should > consider 'hop'... (weak humour, 'a hop, skip and a jump' being an > English idiom meaning a short distance)). Maybe skip would be better, but there will be no problems with something like patents? I mean database which name beginning with big letter «O»? As i know, it has Index Skip Scan.
