What is Sharding in MongoDB?

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Sharding distributes data across multiple machines by partitioning collections on a shard key . The way MongoDB scales horizontally beyond a single server's capacity. Shard key — chosen at collection level; determines which shard a document lives on. Pick carefully — hard to change. Chunks — data partitioned into chunks; balanced across shards automatically. mongos router — routes queries to the right shard; clients only talk to mongos. Config servers — metadata replica set tracking which chunk lives where. Hashed vs ranged — hashed gives even distribution; ranged gives query locality. Use only when needed — adds complexity; vertical scaling is simpler if it fits. Know the three components: shards, config servers, mongos. Shard key selection is the most critical decision — high cardinality + even distribution + query pattern alignment. Ranged vs hashed sharding trade-offs. Sharding is for datasets too large for a single server. Each shard is a replica set.