Re: knngist - 0.8

Robert, it is great you are taking this on.  This is really a well-known
area of the code for you, but not so much for Teodor and Oleg, so I am
sure they appreciate your assistance.

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Robert Haas wrote:
> On Sat, Oct 16, 2010 at 9:54 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> >> Thinking about it that way, perhaps we could add an integer column
> >> amop_whats_it_good_for that gets used as a bit field. ?That wouldn't
> >> require changing the index structure, although it might break some
> >> other things.
> >
> > I gave this a shot (though I called it amoppurpose rather than
> > amop_whats_it_good_for) and I think it's a reasonable way to proceed.
> > Proof-of-concept patch attached. ?This just adds the column (using the
> > existing padding space), defines AMOP_SEARCH and AMOP_ORDER, and makes
> > just about everything ignore anything not marked AMOP_SEARCH,
> > attached. ?This would obviously need some more hacking to pay
> > attention to AMOP_ORDER where relevant, etc. and to create some actual
> > syntax around it. ?Currently CREATE OPERATOR CLASS / ALTER OPERATOR
> > FAMILY have this bit:
> >
> > OPERATOR strategy_number ( op_type [ , op_type ] )
> >
> > knngist-0.9 implements this:
> >
> > [ORDER] OPERATOR strategy_number ( op_type [, op_type ] )
> >
> > ...but with the design proposed above that's not quite what we'd want,
> > because amoppurpose is a bit field, so you could have one or both of
> > the two possible purposes. ?Perhaps:
> >
> > OPERATOR strategy_number ( op_type [ , op_type ] ) [ FOR { SEARCH |
> > ORDER } [, ...] ]
> >
> > With the default being FOR SEARCH.
> 
> Slightly-more-fleshed out proof of concept patch attached, with actual
> syntax, documentation, and pg_dump support added.  This might be
> thought of as a subset of the builtin_knngist_core patch, without the
> parts that make it actually do something useful (which is mostly
> match_pathkey_to_index - which I'm still rather hoping to abstract in
> some way via the access method interface, though I'm currently unsure
> what the best way to do that is).
> 
> I notice that builtin_knngist_core checks whether the return type of
> an ordering operator has a built-in btree opclass.  I'm not sure
> whether we should bother checking that, because even if it's true I
> don't think there's anything preventing it from becoming false later.
> I think it's probably sufficient to just check this condition at plan
> time and silently skip trying to build knn-type index paths if it's
> not met.
> 
> -- 
> Robert Haas
> EnterpriseDB: http://www.enterprisedb.com
> The Enterprise PostgreSQL Company

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--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + It's impossible for everything to be true. +