Re: lexemes in prefix search going through dictionary modifications

On Tue, 2011-10-25 at 19:27 +0200, Florian Pflug wrote:

> Assume, for example, that the postgres mailing list archive search used
> tsearch (which I think it does, but I'm not sure). It'd then probably make
> sense to add "postgres" to the list of stopwords, because it's bound to
> appear in nearly every mail. But wouldn't you want searched which include
> 'postgres*' to turn up empty? Quite certainly not.

That improves recall for "postgres:*" query and certainly doesn't help
other queries like "post:*". But more importantly it affects precision
for all queries like "a:*", "an:*", "and:*", "s:*", 't:*', "the:*", etc
(When that is the only search it also affects recall as no row matches
an empty tsquery). Since stopwords are smaller, it means prefix search
for a few characters is meaningless. And I would argue that is when the
prefix search is more important -- only when you know a few characters.

-Sushant.