- When you plan to create a Couchbase Server cluster, perhaps the most common (and important) question that comes up is:
- How many nodes do I need and what size do they need to be?
- Check Sizing Guidelines for detailed information.
- RAM is allocated to Couchbase Server in two configurable quantities: Server Quota and Bucket Quota
- The Server Quota, is the RAM that is allocated to the server when Couchbase Server is first installed. This sets the limit of RAM allocated by Couchbase for caching data for all buckets and is configured on a per-node basis. The Server Quota is initially configured in the first server in your cluster is configured, and the quota is identical on all nodes. For example, if you have 10 nodes and a 16GB Server Quota, there is 160GB RAM available across the cluster
- The Bucket Quota is the amount of RAM allocated to an individual bucket for caching data. Bucket quotas are configured on a per-node basis, and is allocated out of the RAM defined by the Server Quota. For example, if you create a new bucket with a Bucket Quota of 1GB, in a 10 node cluster there would be an aggregate bucket quota of 10GB across the cluster
Below diagram shows that adding new nodes to the cluster expands the overall RAM quota and the bucket quota, increasing the amount of information that can be kept in RAM.
- The Bucket Quota is used by the system to determine when data should be ejected from memory. Bucket Quotas are dynamically configurable within the limit of your Server Quota
- The Server Quota is also dynamically configurable, but care must be taken to ensure that the nodes in your cluster have the available RAM to support your chosen RAM quota configuration.