Couchbase 4.5 introduces enhancements to its indexing capabilities with features like exclusive in-memory secondary indexes using the memdb storage engine and a high-performance consistency model called "AT_PLUS." These improvements provide developers with finer control over data consistency during queries, allowing for efficient handling of mutations by using mutation sequence IDs. The AT_PLUS consistency model, which requires enabling mutation tokens, offers significant performance gains by synchronizing queries with specific data mutations, reducing latency and resource usage. Couchbase's global secondary indexes remain user-definable with the N1QL language and continue to support flexible query configurations, with options for default, request plus, and high-performance consistency. The update aims to enhance the developer experience and system performance, encouraging users to explore the new features by downloading Couchbase 4.5.