Couchbase and TiDB are both distributed databases with vector search capabilities as add-ons, making them suitable for AI applications that require efficient similarity searches. Couchbase is a NoSQL document-oriented database that can store vector embeddings within JSON structures, while TiDB is a SQL database with hybrid transactional and analytical processing (HTAP) capabilities. Key differences between the two include their search methodology, data handling, scalability and performance, flexibility and customization, integration and ecosystem, ease of use, cost considerations, and security features. When choosing between Couchbase and TiDB for vector search, it's essential to evaluate your specific data management needs and existing infrastructure.