A key-value store is a database model where each item is a unique key mapped to a value, and you read or write the value by supplying its key. The database usually treats the value as opaque data.
Why it matters
The model is simple, so lookups are extremely fast and the data splits cleanly across servers by key. It fits caches, sessions, feature flags, and shopping carts. The limitation is querying: you generally cannot search by value contents or join across items without extra structures you build yourself.
Example
session:9f3a -> {"user_id": 42, "expires": 1760000000}
cart:42 -> [{"sku":"A-100","qty":2}]
flag:new-ui -> "true"Each line is one key and its value.
Common mistakes
- Designing keys with no naming convention, which makes cleanup and debugging painful.
- Trying to run ad hoc queries on values, which this model does not support well.
- Using a hot key that receives most of the traffic and overloads one node.
Related
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