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From: Markus Schaber <schabi@logix-tt.com>
To: pgsql-performance@postgresql.org
Cc: pgsql-hackers@postgresql.org
Subject: Re: qsort again (was Re: [PERFORM] Strange Create Index
Date: Thu, 16 Feb 2006 23:33:48 +0100
Message-ID: <43F4FDCC.2000204@logix-tt.com> (raw)
In-Reply-To: <1140128256.9076.254.camel@archimedes>
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	<43F481CD.2010509@logix-tt.com>
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	<29277.1140110108@sss.pgh.pa.us>
	<1140128256.9076.254.camel@archimedes>

Hi, Mark,

Mark Lewis schrieb:

> It seems that instead of maintaining a different sorting code path for
> each data type, you could get away with one generic path and one
> (hopefully faster) path if you allowed data types to optionally support
> a 'sortKey' interface by providing a function f which maps inputs to 32-
> bit int outputs, such that the following two properties hold:
> 
> f(a)>=f(b) iff a>=b
> if a==b then f(a)==f(b)

Hmm, to remove redundancy, I'd change the <= to a < and define:

if a==b then f(a)==f(b)
if a<b  then f(a)<=f(b)

> Data types which could probably provide a useful function for f would be
> int2, int4, oid, and possibly int8 and text (at least for SQL_ASCII).

With int2 or some restricted ranges of oid and int4, we could even
implement a bucket sort.

Markus



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