From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Jay Levitt <jay(dot)levitt(at)gmail(dot)com> |
Cc: | PG Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Designing an extension for feature-space similarity search |
Date: | 2012-02-16 19:34:34 |
Message-ID: | 14004.1329420874@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Jay Levitt <jay(dot)levitt(at)gmail(dot)com> writes:
> Perfect. Composite types are exactly what I need here; the application can
> declare its composite type and provide distance functions for each member,
> and the extension can use those to calculate similarity. How do I introspect
> the composite type's pg_class to see what it contains? I assume there's a
> better way than SPI on system catalogs :)
Definitely. Take a look at record_out, record_cmp, and sibling
functions on generic composites (src/backend/utils/adt/rowtypes.c).
You might or might not feel like wiring in more assumptions than those
have about the possible contents of the record type.
regards, tom lane
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