Hi, On Thu, 16 May 2024, 17:40 Bowen Song via user, <user@cassandra.apache.org> wrote:
> 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... :( Bye, Gábor AUTH
