Where can I change levensthein_max_length? Janek Sendrowski Von: "Szymon Guz" <mabew...@gmail.com> An: "Tom Lane" <t...@sss.pgh.pa.us> Betreff: Re: [GENERAL] Levenshtein Distance with more than 255 characters On 6 September 2013 08:47, Tom Lane <t...@sss.pgh.pa.us> wrote:
> Szymon Guz <mabew...@gmail.com> writes: > > On 6 September 2013 01:00, Janek Sendrowski <jane...@web.de> wrote: > >> I'm searching for an optimized Levenshtein Distance like Postgresql's. > My > >> problem is that I want to compare strings with a length over 255 > characters. > >> Does anyone know a solution? > > > I'm not sure there is anything different from what you've found in > > core/contribs. But you can always use pg/plpython or pg/plperl procedure > > with some external library calculating the distance. > > Well, you could just rebuild the fuzzystrmatch module with a different > value for MAX_LEVENSHTEIN_STRLEN. The comments in the code note that the > comparison cost is roughly O(N^2) in the string length, and the reason for > having a limit at all is to ensure the function runtime doesn't get out of > hand --- but it seems likely to me that 255 is an unnecessarily > conservative limit. If you wanted to do a few tests and report back on > just how slow it can get, we might be persuaded to raise the stock > setting. > > regards, tom lane > I've checked that and I think we could raise the limit without any problem I've set #define MAX_LEVENSHTEIN_STRLEN 255 * 255 I was using the levenshtein function comparing two strings of the same length Strings length: 640 Difference: 531 Time: 2.5ms Strings length: 1920 Difference: 1258 Time: 20ms Strings length: 5760 Difference: 1811 Time: 146ms regards, Szymon -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
