Re: strpos() && KMP

Added to TODO:

> * Implement Boyer-Moore searching in strpos()
>
>   http://archives.postgresql.org/pgsql-patches/2007-08/msg00012.php


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Pavel Ajtkulov wrote:
> Hello,
>
> this patch allow to use Knuth-Morrison-Pratt algorithm for strpos() function
> (see Cormen et al. Introduction to Algorithms, MIT Press, 2001).
>
> It also works with multibyte wchar.
>
> In worst case current brute force strpos() takes O(n * m) (n && m is length of strings)
> time (example: 'aaa...aaab' search in 'aaa...aaa').
> KMP algo always takes O(n + m) time.
> To check this someone need to create a table with one text attribute, and insert several thousands
> record 'aa..aa'(for example, with lenght = 1000) . After execute "select count(*) from test where
> strpos(a, 'aaa....aab') > 0;" on current and modified version.
>
> Also, I advise to use "select .. where strpos(att, 'word') > 0;" instead "select .. where attr like '%word%'"
> (strpos must be faster than regex).
>
> In general, this belongs to artificial expressions. In natural language KMP is equal (execution time)
> current strpos() nearly.
>
>
> ----
> Ajtkulov Pavel
> ajtkulov@acm.org
>
> P. S. Sorry for prime English.

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