CODEWITHSUNDEEP
cassandracassandra-2.0
Aftab
Aftab

Reputation: 938

How to add new nodes in Cassandra with different machine configuration

I have 6 cassandra nodes in two datacenters with 16GB of memory and 1TB HD drive.

Now I am adding 3 more nodes with 32GB of memory. will these machines will cause overhead for existing machines ( May be in token distribution )? if so please suggest how to configure these machine to avoid those problems.

Thanks in advance.

Upvotes: 1

Views: 186

Answers (1)

Aleksandar Stojadinovic
Aleksandar Stojadinovic

Reputation: 5049

The "balance" between nodes is best regulated using vnodes. If you recall (if you don't, you should read about it), the ring that Cassandra nodes form is actually consisted out of virtual nodes (vnodes). Each node in the ring has a certain portion of vnodes, which is set up in the Cassandra configuration on each node. Based on that number of vnodes, or rather the proportion between them, the amount of data going to those nodes is calculated. The configuration you are looking for is num_tokens. If you have similarly powerful machines, than an equal vnode number is available. The default is 256.

When adding a new, more powerful machine, you should assign a greater number of vnodes to it. How much? I think it's hard to tell. It's unwise to give it twice more, only be looking at the RAM, since those nodes will have twice as many data than the others. Than you might expect more IO operations on them (remember, you still have the same HDD) and CPU utilization (and the same CPU). You might want to take a look at this answer also.

Upvotes: 3

Related Questions