Re: BUG #8354: stripped positions can generate nonzero rank in ts_rank_cd

Would someone please comment on this text search bug report? Thanks.

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On Fri, Aug 2, 2013 at 07:03:42AM +0000, alex(at)hill(dot)net(dot)au wrote:
> The following bug has been logged on the website:
>
> Bug reference: 8354
> Logged by: Alex Hill
> Email address: alex(at)hill(dot)net(dot)au
> PostgreSQL version: 9.2.4
> Operating system: OS X 10.8.4 Mountain Lion
> Description:
>
> Hi all,
>
>
> The docs for ts_rank_cd state:
>
>
> "This function requires positional information in its input. Therefore it
> will not work on "stripped" tsvector values — it will always return zero."
>
>
> However if a tsvector contains some stripped lexemes and some non-stripped,
> ts_rank_cd will rank extents including the non-stripped values.
>
>
> For example, this evaluates to zero as expected:
>
>
> SELECT ts_rank_cd(strip(to_tsvector('text search')),
> plainto_tsquery('text search'))
>
>
>
>
> But this doesn't:
>
>
> SELECT ts_rank_cd(to_tsvector('text') || strip(to_tsvector('search')),
> plainto_tsquery('text search'))
>
>
>
>
> I think this is a bug, if not in the code then in the documentation, which
> isn't clear on what happens when stripped and positioned lexemes are mixed
> in one tsvector.
>
>
> I would prefer that stripped lexemes were completely ignored by ts_rank_cd:
> my use case is using this as a fifth pseudo-weight, which matches a @@ query
> but doesn't add to a ts_rank_cd ranking.
>
>
> What do you think?
>
>
> Cheers,
> Alex
>
>
>
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