On Tue, Nov 30, 2010 at 2:50 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> In the current KNNGIST patch, the indexable ORDER BY clauses are
> transmitted to the executor by cramming them in with the index qual
> conditions (the IndexScan plan node's indexqual list), from whence
> they become part of the ScanKey array passed to the index AM.
> Robert complained that this was an ingenious way to minimize the
> number of lines touched by the patch but utterly ugly from any other
> standpoint, and I quite agree. An ORDER BY clause is a completely
> different thing from a WHERE qual, so mixing them together doesn't
> seem like a good idea.
> However, if we hold to that principle then we need to modify the indexAM
> API to pass the ordering operators separately. This is no big deal as
> far as the built-in AMs are concerned, particularly because 3 of the 4
> need only assert that the additional list is empty. The only reason it
> would be a problem is if there were third-party index AMs that would be
> affected to a larger degree; but I don't know of any. Does anyone have
> an objection to that?
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