Ejection is a mechanism used with Couchbase buckets, and is the process of removing data from RAM to provide room for the active and more frequently used information and is a key part of the caching mechanism. Ejection is automatic and operates in conjunction with the disk persistence system to ensure that data in RAM has been persisted to disk and can be safely ejected from the system.
The system ensures that the data stored in RAM will already have been written to disk, so that it can be loaded back into RAM if the data is requested by a client. Ejection is a key part of keeping the frequently used information in RAM and ensuring there is space within the Couchbase RAM allocation to load that data back into RAM when the information is requested by a client.
For Couchbase buckets, data is never deleted from the system unless a client explicitly deletes the document from the database or the expiration value for the document is reached. Instead, the ejection mechanism removes it from RAM, keeping a copy of that information on disk.