No *guarantees* on collision, but yes, it is a deterministic mapping and you won't see collisions in that range (provided you choose enough bits).
See MurmurHash here: http://en.wikipedia.org/wiki/MurmurHash and to understand collision probabilities, read this: http://en.wikipedia.org/wiki/Birthday_problem On Mon, Jul 21, 2014 at 7:55 PM, Mingtao Zhang <[email protected]> wrote: > Thank you all! > > Sorry, I think 'consistent hashing' is wrong word. > > For my use case, I need to store this 'prefix' (either hashed/not) into > another table. > > Will this murmur hashing guarantee next time same string will map to same > bytes? And no collision for around 2^10 records? > > Mingtao Sent from iPhone > > > On Jul 21, 2014, at 10:28 PM, Ishan Chhabra <[email protected]> > wrote: > > > > Mingtao, > > If I understand correctly, you want to prefix the key with a hash (as > > mentioned in the book) to get a good distribution. Use MurmurHash (there > is > > an implementation in HBase code itself) as it is fast and gives a uniform > > distribution. > > > > "Consistent Hashing" is not the correct term to use here if I understand > > your intent correctly. > > > > > >> On Mon, Jul 21, 2014 at 2:44 PM, Liam Slusser <[email protected]> > wrote: > >> > >> MD5 isn't a consistent hashing algorithm. Consistent hashing is a > scheme > >> that provides a hash table functionality in a way that the adding or > >> removing of one slot does not significantly change the mapping of keys > to > >> slots. With that said, a lot of consistent hashing algorithms USE > >> md5...but it alone won't get you all the way there. > >> > >> Some light bedtime reading: > >> http://en.wikipedia.org/wiki/Consistent_hashing > >> > >> liam > >> > >> > >> On Mon, Jul 21, 2014 at 7:18 AM, Mingtao Zhang <[email protected]> > >> wrote: > >> > >>> Hi, > >>> > >>> I am trying to find a consistant hasing algorithm for the first portion > >> of > >>> the row key. > >>> > >>> I saw the document/book that MD5 is mentioned everything. > >>> > >>> But I have trouble to persuade myself that MD5 ( > >>> http://en.wikipedia.org/wiki/MD5) is considered as consistant hasing. > >>> > >>> Could any of you point me to the library contains the hashing you are > >>> using? > >>> > >>> Thanks in advance! > >>> > >>> Best Regards, > >>> Mingtao > > > > > > > > -- > > *Ishan Chhabra *| Rocket Scientist | RocketFuel Inc. > -- *Ishan Chhabra *| Rocket Scientist | RocketFuel Inc.
