Replication & read preferences in MongoDB

 1. Replication Replication means copying data across multiple servers . MongoDB uses something called a Replica Set How it works: Primary node → handles all writes Secondary nodes → copy data from primary Example: Server 1 → Primary Server 2 → Secondary Server 3 → Secondary All data is duplicated 🔹 Why Replication is Used High availability (if one server fails) Data redundancy Disaster recovery 🔹 Failover If primary fails: One secondary becomes new primary automatically This ensures system keeps running 🔹 2. Read Preferences Read preference decides from which node data is read . 🔹 Types of Read Preferences 1. primary Read only from primary Most consistent data Default mode 2. primaryPreferred Read from primary, fallback to secondary 3. secondary Read only from secondary Reduces load on primary 4. secondaryPreferred Prefer secondary, fallback to primary 5. nearest Read from closest node (lowest latency) 🔹 Why Read Preferences Matter Improve performance Reduce load on primary Balance traffic Important Note Primary → always up-to-date Secondary → may have slight delay (eventual consistency) Simple Understanding Replication → copy data to multiple servers Read preference → choose where to read from