Distributed systems are crucial for vector search applications, offering scalability, fault tolerance, enhanced performance, and global accessibility. Consistency is a key principle in distributed systems, ensuring that data remains accurate across all replicas. The fully distributed Milvus vector database offers Tunable Consistency through its unique architecture, allowing users to scale out data writing while maintaining consistency without additional tools. Consistency levels in Milvus include Eventual, Session, Bounded, and Strong. Eventual consistency ensures that data will eventually be consistent across all replicas, prioritizing speed over immediate data updates. Session consistency maintains up-to-date data within a single session, while Bounded Consistency forces instances and replicas to sync within a certain period. Strong consistency ensures immediate data availability but comes with increased latency. Understanding the levels of consistency is essential for building resilient, high-performing applications that utilize distributed systems.