Couchbase 5.5 introduced an Eventing service that allows developers to write JavaScript functions to execute upon changes to data, referred to as mutations, which include inserts, updates, merges, and deletions. These eventing functions, integrated with N1QL, enable the automation of business process workflows by executing procedural business logic with immediate data access. The functions can be invoked for each data mutation, allowing developers to manage execution times based on the number of mutations. The service supports various use cases, such as maintaining data integrity, synchronizing secondary data, and handling cascade deletes. Developers can leverage N1QL statements within the functions to perform operations like creating indexes, managing referential data, and executing periodic data quality checks. The functionality is documented extensively in Couchbase's blogs and documentation, providing developers with resources to implement eventing strategies effectively.