On 6 September 2013 08:47, Tom Lane <tgl@xxxxxxxxxxxxx> wrote:
Szymon Guz <mabewlun@xxxxxxxxx> writes:
> On 6 September 2013 01:00, Janek Sendrowski <janek12@xxxxxx> 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 inWell, you could just rebuild the fuzzystrmatch module with a different
> core/contribs. But you can always use pg/plpython or pg/plperl procedure
> with some external library calculating the distance.
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
