Question 1

What's the difference between sharding and partitioning?

Accepted Answer

Partitioning usually means splitting a table into parts within the same database system (often on the same server or cluster) and the database manages it. Sharding is a form of horizontal partitioning where data is split across multiple separate database instances (shards). With sharding, your application or a routing layer often needs to know which shard holds the data.

Question 2

When should I use sharding?

Accepted Answer

Consider sharding when a single database instance can’t meet your needs for storage size, write throughput, or concurrent traffic, and vertical scaling (bigger hardware) or read replicas aren’t enough. Sharding is most useful when you have a clear shard key (like user_id, tenant_id, or region) that spreads load evenly and most queries can be routed to a single shard.

Question 3

How much does sharding cost?

Accepted Answer

Sharding usually increases cost because you run multiple database instances instead of one. Costs include: (1) additional compute and storage for each shard, (2) extra replicas for high availability per shard, (3) networking and cross-shard data transfer (especially across regions), (4) operational overhead (monitoring, backups, schema changes, rebalancing), and (5) potential need for middleware or a routing service. The exact cost depends on shard count, instance sizes, replication strategy, and how often you move or rebalance data.

Sharding

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