I don't believe that there has been any reports of collisions, but if. You are concerned you could use the SHA-1 for generating the hash. Relatively speaking, SHA-1is slower, but still fast enough for most applications.
Don't know if it's speed relative to an MD5 and string cat, but it should yield a smaller key.
Sent from a remote device. Please excuse any typos...
On Jul 20, 2012, at 11:31 AM, Damien Hardy <[EMAIL PROTECTED]> wrote:
> Le 20/07/2012 18:22, Jonathan Bishop a écrit :
>> I know it is a commonly suggested to use an MD5 checksum to create a row
>> key from some other identifier, such as a string or long. This is usually
>> done to guard against hot-spotting and seems to work well.
>> My concern is that there no guard against collision when this is done - two
>> different strings or longs could produce the same row-key. Although this is
>> very unlikely, it is bothersome to consider this possibility for large
>> So what I usually do is concatenate the MD5 with the original identifier...
>> MD5(id) + id
>> which assures that the rowkey is both randomly distributed and unique.
>> Is this necessary, or is it the common practice to just use the MD5
>> checksum itself?
> Hello Jonathan,
> md5(id)+id is the good way to avoid hotspotting and insure uniqueness.
> md5(id)+id could be an other way to limit randomness of the rowid on
> 16 values
> You can now combine (with OR logic) 16 filters in a scanner (on for each
> letter available in md5 digest)
> it limits the balance on 16 potentials regions olso.