On Wed, 2012-09-05 at 13:23 +1200, aaron morton wrote:
> > I believe the question is why is the maximum 2**127 and not
> > 0xffffffffffffffff
oops - I got the wrong number of digits there.
> The maximum is the size of the digest created by MD5.
(I may be mistaken) - isn't the range of MD5 values
0 <= hash < (2**128)
?
If you're dropping one bit to store as a signed integer to give 127 bits
of entropy then it would be in the range:
0 <= hash < (2**127)
but the range being checked is:
0 <= hash <= (2**127)
> Does that answer the question?
I meant that what the OP spotted was it's an inclusive maximum <=
0 <= hash <= 2**127 gives (2**127) + 1 different values, and is
mathematically the clock-arithmetic (cyclic) group:
Z/(2**127 + 1) [0]
I _believe_ the issue is actually the other way around in
AbstractHashedPartitioner (upper and lower bounds are exclusive) - but
the comments are incorrect.
i.e. both the code and the comments have off-by-one errors.
{{{
if (i.compareTo(ZERO) < 0)
throw new ConfigurationException("Token must be >= 0");
if (i.compareTo(MAXIMUM) > 0)
throw new ConfigurationException("Token must be <= 2**127");
}}}
The comments imply that 0 and 2**127 are both valid tokens (which they
shouldn't be).
The code does exclusive comparisons and excludes the value 0 though.
Tim
>
[0] I believe the OP mistyped that as Z/(127+1)
>
>
> -----------------
> Aaron Morton
> Freelance Developer
> @aaronmorton
> http://www.thelastpickle.com
>
> On 3/09/2012, at 8:20 PM, Tim Wintle <[email protected]> wrote:
>
> > On Tue, 2012-08-28 at 16:57 +1200, aaron morton wrote:
> > > Sorry I don't understand your question.
> > >
> > > Can you explain it a bit more or maybe someone else knows.
> >
> > I believe the question is why is the maximum 2**127 and not
> > 0xffffffffffffffff
> >
> > Tim
> >
> > >
> > > Cheers
> > >
> > > -----------------
> > > Aaron Morton
> > > Freelance Developer
> > > @aaronmorton
> > > http://www.thelastpickle.com
> > >
> > > On 27/08/2012, at 7:16 PM, Romain HARDOUIN
> > > <[email protected]> wrote:
> > >
> > > >
> > > > Thank you Aaron.
> > > > This limit was pushed down in RandomPartitioner but the question
> > > > still exists...
> > > >
> > > >
> > > > aaron morton <[email protected]> a écrit sur 26/08/2012
> > > > 23:35:50 :
> > > >
> > > > > > AbstractHashedPartitioner
> > > > > does not exist in the trunk.
> > > > > https://git-wip-us.apache.org/repos/asf?p=cassandra.git;
> > > > > a=commitdiff;h=a89ef1ffd4cd2ee39a2751f37044dba3015d72f1
> > > > >
> > > > >
> > > > > Cheers
> > > > >
> > > > > -----------------
> > > > > Aaron Morton
> > > > > Freelance Developer
> > > > > @aaronmorton
> > > > > http://www.thelastpickle.com
> > > > >
> > > > > On 24/08/2012, at 10:51 PM, Romain HARDOUIN
> > > > > <[email protected]> wrote:
> > > > >
> > > > > >
> > > > > > Hi,
> > > > > >
> > > > > > AbstractHashedPartitioner defines a maximum of 2**127 hence
> > > > > > an
> > > > > order of (2**127)+1.
> > > > > > I'd say that tokens of such partitioners are intented to be
> > > > > distributed in Z/(127), hence a maximum of (2**127)-1.
> > > > > > Could there be a mix up between maximum and order?
> > > > > > This is a detail but could someone confirm/invalidate?
> > > > > >
> > > > > > Regards,
> > > > > >
> > > > > > Romain
> > > > >
> > >
> >
> >
>
>
