CODEWITHSUNDEEP
cassandra
jie ren
jie ren

Reputation: 11

The contact between Replication factor and Resource Usage

I am a Cassandra user in china. Recently we want to use Cassandra in our production environment. But I don't know the impact of data replica factor and resource consumption. My stress test show that 3 replication factor use three times more resources than 1 replication factor. But I'm not sure it's right. So, I would like to ask if there is a formula for replication factor and resource consumption? Or has anyone ever tested it?

I'm very grateful if anyone can reply me;

Upvotes: 1

Views: 54

Answers (2)

LetsNoSQL
LetsNoSQL

Reputation: 1538

Cassandra is distributed database so it stores the data based on partition and hash algorithm. We can configure replica of our data based on requirement and application nature. Default Cassandra cluster with minimum 3 node recommended for production but you should use or configure the replication factor(replica/copy of data) totally on your wish.

If you use 3 node cluster with RF=3 then your data will be distributed on each node (approx 1/3 data on each node). We need to consider the resource here for all 3 nodes like disk, CPU, Memory, I/O etc equally for better performance. However, we can tune multiple things(like consistency, compaction, network, OS) inside the Cassandra to improve the performance and resource effective. 3 copy of data will use more memory and disk as compared to 1 copy of data. But if you consider availability and performance you should use at least 2 copy of data. you can refer below link for more details regarding RF calculation etc:- https://www.ecyrd.com/cassandracalculator/

Upvotes: 0

Aaron
Aaron

Reputation: 57748

First of all, RF=3 means you need at least three servers (obviously). But really, it depends on what you mean by "resources." If that's mainly referring to disk space, then "yes" setting a RF=3 will use 3x the disk space that a single copy (RF=1) would.

So why would you want that? Because supporting data loads in highly-available (HA) scenarios is what Cassandra does really well. This means that Cassandra needs to be able to continue to serve requests if a node should fail. Achieving that means setting RF>1.

As for the remaining resources, if you're referring to network, CPU & RAM as well, then the answer is "it depends." An application can choose to query at different consistency levels, such as ONE, QUORUM, or ALL (and others). For ONE, it does just what it says: an operation (read or write) waits for acknowledgement from a single node.

So if an app is querying at a consistency of ONE, the answer is "no," it won't use three times the resources if RF=3.

Upvotes: 1

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