Top-k optimizations?

Folks,

As this came up in a work situation, I was wondering a little bit
about the top-k issue.  Right now, top-k is implemented (most easily,
I think) via a SELECT with a LIMIT and no OFFSET.  3 questions arise
from this.

1.  Are there currently any optimizations specific to top-k in
PostgreSQL?  If so, what are they?

2.  What kinds of top-k optimizations *can't* be part of PostgreSQL
(things that would break MVCC, e.g.)?

3.  What kinds of top-k optimizations might (eventually) be included
in PostgreSQL?

Hoping this stimulates some friendly & informative discussion... :)

Cheers,
D
-- 
David Fetter david@fetter.org http://fetter.org/
phone: +1 510 893 6100   mobile: +1 415 235 3778

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