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From Eric Stevens <migh...@gmail.com>
Subject Re: Node tokens / data move
Date Tue, 16 Jul 2013 12:35:26 GMT
>
> vnodes currently do not brings any noticeable benefits to outweight trouble


The main advantage of vnodes is that it lets you have flexibility with
respect to adding and removing nodes from your cluster without having to
rebalance your cluster (issuing a lot of moves).  A shuffle is a lot of
moves too, so the only reason to do this is if you've discovered that the
random allocation of vnodes has managed to leave an unbalanced cluster (one
node either has an unusually large load, or an unusually small one).

Shuffling isn't something you should be doing as a matter of course, and
with 256 vnodes per server and 3+ servers, the chances of a brokenly
unbalanced cluster is more likely the cause of bad data partitioning
(extremely unbalanced row sizes) than of vnode token placement.  With
unbalanced rows, nothing will solve balance problems except finding a
different way to partition your data across rows.



On Mon, Jul 15, 2013 at 7:10 AM, Radim Kolar <hsn@filez.com> wrote:

>
>  My understanding is that it is not possible to change the number of
>> tokens after the node has been initialized.
>>
> that was my conclusion too. vnodes currently do not brings any noticeable
> benefits to outweight trouble. shuffle is very slow in large cluster.
> Recovery is faster with vnodes but i have very few node failures per year.
>

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