Thanks Rob, I didn't realize that you could use the initial_token when using
vnodes.
I see what you mean now that with RF=N having multiple vnodes is not
actually achieving anything unless we add further nodes, we hadn't really
considered that when we initially installed with the default yaml file.
For a small cluster, e.g. 9 nodes with RF=3 would you actually recommend
using vnodes at all and if so how many?
Phil
Robert Coli-3 wrote
> On Thu, May 22, 2014 at 4:31 AM, Phil Luckhurst <
> phil.luckhurst@
>> wrote:
>
>> We have a 3 node 2.0.7 cluster with RF=3. At the moment these are
>> configured
>> to have the default 256 vnodes we'd like to try reducing that to see what
>> effect it has on some of our CQL query times.
>>
>
> Because you have RF=N, all nodes have all data. This means that it is
> actually irrelevant how many vnodes (or nodes) you have, you just get lose
> from using them at all.
>
> However to reduce the number of vnodes to a number that is ok in your case
> but also might be reasonable when you have RF != N, you can just :
>
> 1) get a list of tokens per node via a one-liner like this :
>
> nodetool info -T | grep Token | awk '{print $3}' | paste -s -d,
>
> 2) modify this list by removing however many tokens you want to get to the
> new number of vnodes
>
> 3) insert this list into the initial_token line of cassandra.yaml on each
> node [1]
>
> 4) rolling re-start nodes with auto_bootstrap:false [2]
>
> My *belief* is that you do not need a step 3.5 "nuke the system keyspace
> and reload schema, potentially with the entire cluster down", but it's
> possible that other nodes may remember your old vnodes unless you do. Test
> in a non-production environment, obviously.
>
> If the above is too complicated and you have the spare hosts, adding 3 new
> nodes and then decommissioning the old ones is a safe and simple way to
> achieve the same goal.
>
> =Rob
> [1] Note that I recommend this as a best practice for the use of vnodes,
> always populate initial_token.
> [2]
> https://engineering.eventbrite.com/changing-the-ip-address-of-a-cassandra-node-with-auto_bootstrapfalse/
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