On Thu, 16 May 2024, 17:40 Bowen Song via user, <user@cassandra.apache.org>

> Replacing nodes one by one in the existing DC is not the same as replacing
> an entire DC.
> For example, if you change from 256 vnodes to 4 vnodes on a 100 nodes
> single DC cluster. Before you start, each node owns ~1% of the cluster's
> data. But after changing 99 nodes, the last remaining node will own ~39% of
> the cluster's data. Will that node have enough storage and computing
> capacity to handle that? Unless you have significantly over-provisioned
> node size, the answer is definitely no. The way to work around this is to
> gradually reduce the vnodes number. E.g. reducing from 256 to 128 will
> require the last node to have 2x the capacity, which is much more doable
> than 39x. To do it this way, you will need to repeat the process to reduce
> vnodes number from 256 to 128, then to 64, 32, 16, 8 and finally 4.
> So, the most significant difference is, how many times do the data need to
> be moved?
Thank you for the explanation, this will help others think about it when
they search about changing num_tokens... :)

I am aware about it, but in my current case there are only 4 nodes, with a
total of maybe ~25GB of data. So, creation of a new DC is more hassle for
me than replace nodes one-by-one.

My question was whether there is a simpler solution. And it looks like
there is no... :(

Gábor AUTH

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