Re: Improving DISTINCT with LooseScan node

> It seems related to this thread? :
> https://www.postgresql.org/message-id/flat/5037A9C5(dot)4030701%40optionshouse(dot)com#5037A9C5(dot)4030701(at)optionshouse(dot)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.