Write concern & read concern in MongoDB

🔹 1. Write Concern Write Concern defines how safely data is written to the database . It decides: How many nodes must confirm the write Whether data is fully saved before success is returned 🔹 Common Write Concern Levels 1. w: 1 (default) Write is acknowledged by primary only Fast  Less safe  2. w: "majority" Write is confirmed by majority of nodes Slower Very safe  3. w: 0 No acknowledgment Very fast Risky 🔹 Extra Options j: true → ensures data is written to disk (journal) wtimeout → timeout for write 🔹 2. Read Concern Read Concern defines how consistent the data is when reading . It decides: Whether you read latest data or possibly stale data 🔹 Common Read Concern Levels 1. local (default)  Reads data from node without guarantee of replication Fast May not be fully consistent 2. majority Reads only data confirmed by majority Strong consistency  3. linearizable Reads most recent data (strict consistency) Slowest Strongest guarantee 🔹 Why They Matter Balance between performance vs data safety Important in distributed systems Simple Understanding Write Concern → how safely data is written Read Concern → how consistent data is read Example Idea Banking app → use majority (safe) Social media → use default (fast)