From: Tom Lane <tgl@sss.pgh.pa.us>
To: Simon Riggs <simon@2ndquadrant.com>
Cc: pgsql-docs@postgresql.org, Oleg Bartunov <oleg@sai.msu.su>
Cc: Teodor Sigaev <teodor@sigaev.ru>
Subject: Re: Normalized Ranking example incorrect in text search
Date: Wed, 14 Nov 2007 14:49:26 -0500
Message-ID: <11985.1195069766@sss.pgh.pa.us> (raw)
In-Reply-To: <11802.1195069042@sss.pgh.pa.us>
References: <1195021491.4378.71.camel@ebony.site>
<11802.1195069042@sss.pgh.pa.us>
I wrote:
> Simon Riggs <simon@2ndquadrant.com> writes:
>> and then gives a query which calculates normalization in an incorrect
>> manner,
> On what basis do you claim that's an incorrect manner? It's exactly
> what is described in the paragraph just before the examples.
... although on reflection, it seems pretty stupid to be recommending
a method that requires two evaluations at each row of an admittedly
expensive function.
Seems like we should add one more normalization flag bit:
32 --- replace computed rank by rank / (rank + 1)
and then the second example would be
SELECT title, ts_rank_cd(textsearch, query, 32 /* rank/(rank+1) */) AS rank
FROM apod, to_tsquery('neutrino|(dark & matter)') query
WHERE query @@ textsearch
ORDER BY rank DESC LIMIT 10;
with no change in the example output.
regards, tom lane
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To: pgsql-docs@postgresql.org
Cc: tgl@sss.pgh.pa.us, simon@2ndquadrant.com, oleg@sai.msu.su, teodor@sigaev.ru
Subject: Re: Normalized Ranking example incorrect in text search
In-Reply-To: <11985.1195069766@sss.pgh.pa.us>
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