userids

UserIDs are identifiers assigned to individual user accounts to uniquely distinguish users within a system. They serve as stable references used for authentication, authorization, auditing, and data relationships. User IDs differ from usernames in that they are typically system-assigned and can remain constant even if a user changes their display name.

Common formats include integers, strings, and universally unique identifiers such as UUIDs or ULIDs. In relational databases, a user_id is often an auto-incrementing integer used as the primary key. In distributed systems and public APIs, opaque IDs like UUIDs provide global uniqueness and reduce predictability, while tokens or claims in authentication protocols may carry a user_id value for downstream services.

Generation and lifecycle considerations include ensuring uniqueness, persistence, and resilience to changes. IDs are usually created at account creation and persist for the account’s lifetime, though some designs support account merges or deactivations. In some architectures, IDs remain stable across migrations or merges to preserve historical data relations.

Security and privacy concerns center on minimizing exposure of identity patterns. Exposing sequential or easily guessable IDs can enable user enumeration. Best practices include using opaque IDs in public interfaces, validating permissions with server-side checks, and avoiding reliance on client-supplied IDs for access decisions. In privacy-sensitive contexts, consider pseudonymous or rotated identifiers and careful logging practices to prevent leakage of user mappings.

Usage notes include serving as foreign keys in related data, supporting data integrity, and helping enforce access controls. In large systems, ID design may influence performance, sharding, and data partitioning, while ensuring that user-related data remains properly linked regardless of username changes or account aliases.