Eviction Strategies

When cache is full (maxSize reached), which entry should be removed?

LRU (Least Recently Used)

Remove the entry that was accessed longest ago.

Access order: A → B → C → A → D
Cache size: 3

State after D:
  A: lastAccess=4 (recent)
  C: lastAccess=3 (recent)
  D: lastAccess=5 (recent)
  B: lastAccess=2 (oldest) ← EVICT

Best for: General purpose, most web applications.

const node = new CacheNode("node-1", {
  maxSize: 1000,
  evictionPolicy: "lru", // default
});

LFU (Least Frequently Used)

Remove the entry with fewest accesses.

Access counts:
  A: accessed 10 times
  B: accessed 2 times  ← EVICT
  C: accessed 8 times

Best for: Workloads with clear "hot" and "cold" keys.

const node = new CacheNode("node-1", {
  maxSize: 1000,
  evictionPolicy: "lfu",
});

FIFO (First In, First Out)

Remove the oldest entry regardless of access.

Insertion order: A → B → C → D
Cache size: 3

After D:
  A: inserted 1st ← EVICT
  B: inserted 2nd
  C: inserted 3rd
  D: inserted 4th

Best for: Simple workloads, streaming data.

const node = new CacheNode("node-1", {
  maxSize: 1000,
  evictionPolicy: "fifo",
});

Comparison

Strategy	Speed	Memory	Use Case
LRU	Fast	Good	General purpose
LFU	Medium	Best	Hot key patterns
FIFO	Fastest	Fair	Simple workloads

TTL (Time To Live)

In addition to eviction, entries can expire automatically:

// Auto-expire after 60 seconds
node.set("session:abc", data, 60000);

// Background sweep every 30 seconds removes expired entries