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From prasenjit mukherjee <prasen....@gmail.com>
Subject Re: random partitioner and key scan
Date Fri, 20 Jul 2012 09:35:15 GMT
Agree to aaron's point. But still I think there are ways to overcome
this problem, as I believe that the row-scan use-case is very
important. One simple ( but expensive ) approach could be to duplicate
the rows with RP tokens on primary node, which will be used only in
case of repairs.

Any thoughts ?

Thanks,
Prasenjit

On 7/20/12, aaron morton <aaron@thelastpickle.com> wrote:
> Repair and token moves work on ranges of Tokens, not row keys. These
> operations need to scan through all the rows in the token range.
>
> Ordering the rows by row key locally would mean that every row on the node
> would have to be scanned to find the ones whose token was in the required
> token range.
>
> Cheers
>
> -----------------
> Aaron Morton
> Freelance Developer
> @aaronmorton
> http://www.thelastpickle.com
>
> On 20/07/2012, at 4:46 AM, prasenjit mukherjee wrote:
>
>> When a request for token change is issued ( via nodetool ) then on
>> what basis a node will move some of its rows to other node, as there
>> will be no way to scan rows based on MD5 hash in a given node ( if the
>> keys are not prefixed with MD5 hash )
>>
>> On Thu, Jul 19, 2012 at 1:43 PM, Patrik Modesto
>> <patrik.modesto@gmail.com> wrote:
>>> Hi Prasenjit,
>>>
>>> I don't see the need to recalculate anything. One key has a one MD5
>>> hash, it doesn't change. Just use the hash to select a node, than just
>>> the plain key. Can you elaborate on the redistribution please?
>>>
>>> Regards,
>>> P.
>>>
>>> On Thu, Jul 19, 2012 at 9:09 AM, prasenjit mukherjee
>>> <prasen.bea@gmail.com> wrote:
>>>> The probem could be while redistributing the tokens. In that case the
>>>> hashes has to be recalculated on each fo the candidate node.
>>>>
>>>> -Thanks,
>>>> Prasenjit
>>>>
>>>> On Thu, Jul 19, 2012 at 12:19 PM, Patrik Modesto
>>>> <patrik.modesto@gmail.com> wrote:
>>>>> Hi,
>>>>>
>>>>> I know that RandomPartitioner does MD5 of a key and the MD5 is then
>>>>> used for key distribution AND key ordering. I was just wondering if
>>>>> it's possible to have RandomPartitioner just for key distribution and
>>>>> OrderedPartitioner just for per-node key ordering. That would solve
>>>>> the often requested key scan feature.
>>>>>
>>>>> Regards,
>>>>> Patrik
>
>

-- 
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