Re: TS: Limited cover density ranking

The rank counts 1/coversize. So bigger covers will not have much impact
anyway. What is the need of the patch?

-Sushant.

On Fri, 2012-01-27 at 18:06 +0200, karavelov(at)mail(dot)bg wrote:
> Hello,
>
> I have developed a variation of cover density ranking functions that
> counts only covers that are lesser than a specified limit. It is
> useful for finding combinations of terms that appear nearby one
> another. Here is an example of usage:
>
> -- normal cover density ranking : not changed
> luben=> select ts_rank_cd(to_tsvector('a b c d e g h i j k'),
> to_tsquery('a&d'));
> ts_rank_cd
> ------------
> 0.0333333
> (1 row)
>
> -- limited to 2
> luben=> select ts_rank_cd(2, to_tsvector('a b c d e g h i j k'),
> to_tsquery('a&d'));
> ts_rank_cd
> ------------
> 0
> (1 row)
>
> luben=> select ts_rank_cd(2, to_tsvector('a b c d e g h i j k a d'),
> to_tsquery('a&d'));
> ts_rank_cd
> ------------
> 0.1
> (1 row)
>
> -- limited to 3
> luben=> select ts_rank_cd(3, to_tsvector('a b c d e g h i j k'),
> to_tsquery('a&d'));
> ts_rank_cd
> ------------
> 0.0333333
> (1 row)
>
> luben=> select ts_rank_cd(3, to_tsvector('a b c d e g h i j k a d'),
> to_tsquery('a&d'));
> ts_rank_cd
> ------------
> 0.133333
> (1 row)
>
> Find attached a path agains 9.1.2 sources. I preferred to make a
> patch, not a separate extension because it is only 1 statement change
> in calc_rank_cd function. If I have to make an extension a lot of code
> would be duplicated between backend/utils/adt/tsrank.c and the
> extension.
>
> I have some questions:
>
> 1. Is it interesting to develop it further (documentation, cleanup,
> etc) for inclusion in one of the next versions? If this is the case,
> there are some further questions:
>
> - should I overload ts_rank_cd (as in examples above and the patch) or
> should I define new set of functions, for example ts_rank_lcd ?
> - should I define define this new sql level functions in core or
> should I go only with this 2 lines change in calc_rank_cd() and define
> the new functions as an extension? If we prefer the later, could I
> overload core functions with functions defined in extensions?
> - and finally there is always the possibility to duplicate the code
> and make an independent extension.
>
> 2. If I run the patched version on cluster that was initialized with
> unpatched server, is there a way to register the new functions in the
> system catalog without reinitializing the cluster?
>
> Best regards
> luben
>
> --
> Luben Karavelov