Re: Google Summer of Code 2008

Oleg Bartunov wrote:
> Jan,
>
> the problem is known and well requested. From your promotion it's not
> clear what's an idea ?
>> Tom Lane wrote:
>>> =?UTF-8?B?SmFuIFVyYmHFhHNraQ==?= <j(dot)urbanski(at)students(dot)mimuw(dot)edu(dot)pl>
>>> writes:
>>>> 2. Implement better selectivity estimates for FTS.

OK, after reading through the some of the code the idea is to write a
custom typanalyze function for tsvector columns. It could look inside
the tsvectors, compute the most commonly appearing lexemes and store
that information in pg_statistics. Then there should be a custom
selectivity function for @@ and friends, that would look at the lexemes
in pg_statistics, see if the tsquery it got matches some/any of them and
return a result based on that.

I have a feeling that in many cases identifying the top 50 to 300
lexemes would be enough to talk about text search selectivity with a
degree of confidence. At least we wouldn't give overly low estimates for
queries looking for very popular words, which I believe is worse than
givng an overly high estimate for a obscure query (am I wrong here?).

Regards,
Jan

--
Jan Urbanski
GPG key ID: E583D7D2

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