sharding key

Definitions

1. The column or value used to determine which shard (partition) of a distributed database stores a given row. Choosing the right sharding key is one of the most consequential architectural decisions in distributed systems — a bad choice leads to hot spots, cross-shard queries, and expensive resharding operations that can take weeks.

   In plain English: The piece of data that decides which slice of a split-up database stores each record — choose poorly and one slice gets overloaded.

   Example: They sharded by user_id, which worked great until one enterprise customer had 10 million rows and their shard became a permanent hot spot.

Related Terms

• foreign key
• normalization
• denormalization