Apache Cassandra and OpenSearch are two options in the vector database space that have evolved to include vector search capabilities as an add-on. Both technologies offer distributed architectures, support for structured and unstructured data, and scalability features. However, they differ in their search methodology, data handling, flexibility, integration with other tools, ease of use, cost considerations, and security features. The choice between Cassandra and OpenSearch should depend on the specific use case, data types, scalability needs, and existing technology stack.