What is the difference between sharding and partitioning?

Sharding and partitioning are both strategies for dividing data to improve scalability and performance, but they operate at different levels and serve distinct purposes. Sharding refers to splitting a dataset horizontally across multiple independent databases or servers (often called shards), each acting as a separate storage node. Partitioning involves organizing data into smaller, more manageable segments within a single database. The key difference is scope: sharding distributes data across systems, while partitioning organizes it within a system.

Partitioning typically divides data based on logical rules, such as ranges, lists, or hash functions, but keeps all partitions under a single database’s control. For example, a table storing sales records could be partitioned by year, with each partition holding data for a specific year. Queries filtering by year would scan only the relevant partition, improving performance without requiring changes to application logic. Database systems like PostgreSQL or MySQL support native partitioning, allowing developers to manage partitions through schema definitions. This approach simplifies maintenance (e.g., archiving old data by dropping a partition) but doesn’t address scalability limits of a single server.

Sharding, in contrast, addresses horizontal scaling by spreading data across multiple machines. For instance, a user database might be sharded by geographic region, with separate shards for North America, Europe, and Asia. Each shard operates independently, often requiring application-level logic to route queries (e.g., directing a user’s request to the correct shard based on their location). While sharding enables handling massive datasets and high traffic, it introduces complexity: joins across shards are inefficient, transactions spanning shards require distributed coordination, and rebalancing shards (e.g., due to uneven growth) can be challenging. Systems like MongoDB automate some aspects of sharding, but developers still need to design shard keys carefully to avoid hotspots.

In summary, partitioning optimizes data management within a single database, while sharding scales systems by distributing data across databases. Partitioning is a tactical tool for performance tuning; sharding is a strategic choice for large-scale distributed systems.