Couchbase handles concurrent access and locking through a combination of document-level locking and optimistic concurrency control.
In Couchbase, each document has a unique identifier and a revision ID (also known as a CAS, or Compare And Swap value). When a client attempts to modify a document, Couchbase checks the CAS value to ensure that the document hasn't been modified by another client since it was last read. If the CAS values match, the modification proceeds, and the CAS value is updated. If the CAS values don't match, it means the document has been modified by another client, and the update is rejected, prompting the client to retry the operation with the latest version of the document.
For scenarios where conflicts are infrequent and can be resolved easily, Couchbase's optimistic concurrency control is effective. However, in cases where conflicts are more common or complex, Couchbase offers document-level locking. When a client starts a write operation on a document, Couchbase locks the document to prevent other clients from modifying it until the operation is complete. This ensures data consistency but can introduce latency if many clients are attempting to modify the same documents simultaneously.
For example, in an e-commerce application, when multiple users try to update the stock of a product simultaneously, Couchbase's concurrency control mechanisms ensure that only one user's update is applied at a time, preventing data inconsistencies.
In the context of cloud services, Couchbase can be deployed on various cloud platforms, including Tencent Cloud, where it can leverage the cloud's scalability and reliability features to handle large volumes of concurrent access and ensure high availability of data.