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Data & Analytics · Intermediate

Sharding

Horizontal partitioning of data across multiple database servers (shards) to scale writes and storage.

Definition

Each shard holds a subset of rows determined by a shard key, using range, hash or directory-based placement. Sharding scales out but complicates cross-shard joins and transactions and risks hotspots when the key is poorly chosen. MongoDB, Cassandra, Spanner and Cosmos DB shard natively.

Exam tip

Sharding is horizontal scaling across servers; partitioning can happen within a single server.

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