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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: OPHF vs. Random
Date Mon, 16 Mar 2009 20:36:16 GMT
The order-preserving partitioner code (not hash-based anymore) is up
now at https://issues.apache.org/jira/browse/CASSANDRA-3.

-Jonathan

On Wed, Mar 11, 2009 at 6:48 PM, Jonathan Ellis <jbellis@gmail.com> wrote:
> Use Random for now.  The OPHF is the same as the old one, i.e., not
> actually OP. :)
>
> I'm pretty convinced at this point that it's impossible to have an
> order-preserving hash that doesn't either (a) impose a relatively
> short key length past which no partitioning is done (i.e., all keys w/
> the same prefix go to the same node) or is (b) very sensitive to key
> length such that the keys with a given length N will not be evenly
> distributed across all nodes. Or both.
>
> So I am working on migrating from pluggable hash functions key ->
> BigInteger, to pluggable partitioning algorithms key -> EndPoint.
> Without the requirement to transform to a numeric value first I think
> I can create an order-preserving distribution that performs well.  (I
> need this for range queries.)
>
> So far I have just laid the foundation, here:
> https://issues.apache.org/jira/browse/CASSANDRA-3
>
> I hope to finish the rest tomorrow.
>
> -Jonathan
>
> On Wed, Mar 11, 2009 at 5:28 PM, Jiansheng Huang <jiansheng.wi@gmail.com> wrote:
>>
>> Which one is better to use? The default is Random.
>>
>> In Avinash's annoucement mail, we have
>> (1) Ability to switch between a random hash and a OPHF. We still have the
>> old (wrong) OPHF in there. I will update it to the corrected one tomorrow.
>>
>> Is correct OPHF in? Thanks.
>>
>

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