Re: [bailey-developers] Features and their design

[Doug C. <cu...@ap...>]

Ning Li wrote:
>>  >  1 Consistent hashing uses hash values because hash values
>>  >   distribute uniformly on the ring. Can we support
>>  >   application-specified keys for the ring?
>>
>>  Seems like we could allow the user to specify their own hash value.
>>  What's the usecase here?
> 
> An example application can be an online email system.
> The keys of a user's emails are prefixed by the user name,
> so a user's emails are located together on the ring. When
> a user searches his/her emails, the query is only sent to
> servers which cover that range, instead of the entire ring.

We could just define doc ids as 128-bit numbers rather than strings. 
Then user-provided hash values wouldn't be a special case.  A 
constructor could convert string ids to 128-bit ids, and also store the 
original string in a field named "id".

128-bits is big enough that we shouldn't see collisions.

http://en.wikipedia.org/wiki/Birthday_attack

By my reading, it would take over a trillion collections of a trillion 
documents each before a collision is probable.

Doug