LRUキャッシュ
A Least Recently Used (LRU) Cache is a type of data structure that stores a limited number of items while efficiently managing their retrieval and storage based on usage history. The primary goal of an LRU Cache is to ensure that the most recently accessed items are kept readily available, while the least recently accessed items are removed when the cache reaches its capacity.
The LRU caching algorithm works on the principle that data which has been accessed recently is more likely to be accessed again in the near future. Thus, when the cache is full and a new item needs to be added, the cache will evict the item that has not been used for the longest period of time. This eviction strategy helps optimize performance, particularly in applications that require frequent access to a limited subset of data, such as ウェブブラウザ, databases, and applications with limited memory resources.
実装
通常、LRUキャッシュはハッシュの組み合わせを使用して実装される map and a doubly linked list. The hash map allows for O(1) average time complexity for both retrieval and insertion of cache items, while the doubly linked list maintains the order of usage. When an item is accessed, it is moved to the front of the list, indicating that it is the most recently used. Conversely, when an eviction occurs, the item at the back of the list—the least recently used item—is removed.
利用例
LRUキャッシュは、さまざまなアプリケーションで広く使用されています。例えば：
- 最近アクセスされたウェブページを保存するウェブキャッシング。
- データベースクエリのキャッシングによる高速化 データ取得.
- 記憶 management オペレーティングシステムでリソース使用を最適化するために。
LRUキャッシュを実装することで、システムは大幅に削減できる latency 高頻度アクセスパターンに対処する際の効率性を向上させる。