expirer

An expirer is a component or service that enforces expiration of items that have a limited lifespan. The term is used in computing and data management to describe agents that remove, invalidate, or flag data once its time-to-live (TTL) has elapsed. Expirer functionality can be embedded in applications, databases, caches, or dedicated background services.

Typically, an expirer attaches a TTL to items such as cache entries, session data, authentication tokens, or retained logs. It monitors time and, when an item’s TTL expires, marks the item as expired, deletes it, or triggers a cleanup callback. Expiration can be performed actively through periodic sweeps or passively through event-driven mechanisms that check validity on access. In distributed systems, expiring may involve coordination across nodes and handling clock skew, latency, and replication delays.

Common domains for expirer use include web caching (evicting stale entries), session stores (removing inactive sessions), token and credential management (invalidating expired tokens), and data retention policies (deleting aged records). Some systems implement lazy expiration, where items are checked for validity when accessed, while others rely on scheduled jobs or background workers to purge expired data.

Design considerations for an expirer include correctness with respect to TTL definitions, performance impact of expiration checks, and consistency in distributed environments. Other related concepts include eviction policies, garbage collection, and lease or lease-expiration mechanisms, which address similar problems of automatic removal or invalidation based on time.