Re: Migrating Cassandra from 3.11.11 to 4.0.0 vs num_tokens

[Elliott Sims]

Won't option 2 in that list potentially cause some pretty severe load
imbalance in most cases?  The last node with 256 tokens will end up with
16x as much data on it as the 16 token nodes, right?

You'd have to mitigate it either by adding 16 new nodes for every one you
replace except the last one, or doing several rounds of replacing every
node with one that has somewhat fewer tokens.

On Sat, Sep 4, 2021, 2:36 AM Erick Ramirez 
wrote:

> It isn't possible to change the tokens on a node once it is already part
> of the cluster. Cassandra won't allow you to do it because it will make the
> data  already on disk unreadable. You'll need to either configure new nodes
> or add a new DC. I've answered an identical question in
> https://community.datastax.com/questions/12213/ where I've provided steps
> for the 2 options. I hope to draft a runbook and get it published on the
> Apache website in the coming days. Cheers!
>

Re: Migrating Cassandra from 3.11.11 to 4.0.0 vs num_tokens

[Anthony Grasso]

Hi Jean,

This is a really good question.

As Erick mentioned, if you want to change your cluster's *num_tokens* to 16
to match the 4.0 default, you will need to perform a datacenter migration.
Feel free to read over this blog post
 written
by The Last Pickle which will provide background details about the process.
The information should follow the Apache website runbook (when published)
fairly closely.

Kind regards,

On Sat, 4 Sept 2021 at 20:45, Jean Tremblay  wrote:

> Great Thank you for the answer and the link!
>
>
> On 4 Sep 2021, at 11:35, Erick Ramirez  wrote:
>
> It isn't possible to change the tokens on a node once it is already part
> of the cluster. Cassandra won't allow you to do it because it will make the
> data  already on disk unreadable. You'll need to either configure new nodes
> or add a new DC. I've answered an identical question in
> https://community.datastax.com/questions/12213/ where I've provided steps
> for the 2 options. I hope to draft a runbook and get it published on the
> Apache website in the coming days. Cheers!
>
>
>

Re: Migrating Cassandra from 3.11.11 to 4.0.0 vs num_tokens

[Jean Tremblay]

Great Thank you for the answer and the link!


> On 4 Sep 2021, at 11:35, Erick Ramirez  wrote:
> 
> It isn't possible to change the tokens on a node once it is already part of 
> the cluster. Cassandra won't allow you to do it because it will make the data 
>  already on disk unreadable. You'll need to either configure new nodes or add 
> a new DC. I've answered an identical question in 
> https://community.datastax.com/questions/12213/ 
>  where I've provided steps 
> for the 2 options. I hope to draft a runbook and get it published on the 
> Apache website in the coming days. Cheers!

Re: Migrating Cassandra from 3.11.11 to 4.0.0 vs num_tokens

[Erick Ramirez]

It isn't possible to change the tokens on a node once it is already part of
the cluster. Cassandra won't allow you to do it because it will make the
data  already on disk unreadable. You'll need to either configure new nodes
or add a new DC. I've answered an identical question in
https://community.datastax.com/questions/12213/ where I've provided steps
for the 2 options. I hope to draft a runbook and get it published on the
Apache website in the coming days. Cheers!

Migrating Cassandra from 3.11.11 to 4.0.0 vs num_tokens

[Jean Tremblay]

Hi,

We are currently running Cassandra 3.11.11 with the default values for 
num_tokens: 256.
We want to migrate to Cassandra 4.0.0 which has default values for num_tokens 
set to 16.

Is it safe to migrate with the default values, i.e. can I leave it set to 16 
when migrating to Cassandra 4.0.0 or is there something special which needs to 
be done?

Thanks for your help.

Cheers

Jean