TS: Limited cover density ranking

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