PerfCache is an API that allows for creation and management of a memory cache. It includes basic cache operations (insert and retrieve), replacement policies, and expiration. Cache entry keys are strings of bytes, and data items are arrays of bytes. Variable length keys and data are supported. The cache itself is implemented as an array. The cache infrastructure includes a directory, mapping cache entry keys to cache array indices, and a sub-system for handling cache entry replacement metadata. The LRU and LFU replacement policies are supported; the replacement metadata management overhead is O(1). PerfCache includes support for synchronization and for cache operation statistics.