Struct TinyLfuEstimator 

pub struct TinyLfuEstimator { /* private fields */ }

Shared W-TinyLFU frequency evidence: one sighting per served request from the serve path, one estimate read per fill-path admission decision and per probation candidate at sweep time.

The counters live in a ShardedCountMinSketch, so a sighting or an estimate locks the one shard its hash routes to. Serve completions and admission reads for different hashes therefore proceed in parallel, and the periodic aging pass touches a single shard rather than the whole array.

Aging runs on one node-wide clock across all shards. Both readers below compare estimates on a shared scale — ProbationAdmission against a node-wide threshold, TinyLfuEviction by ranking candidates from different shards against each other — so counters are only meaningful if each is caught up to that one clock when it is read. A clock per shard would age at a rate set by key skew and put the two readers on scales that cannot be compared at all.

Implementations

impl TinyLfuEstimator

pub fn new(sketch_bytes: usize) -> Self

Size the sketch to roughly sketch_bytes of counters: one u8 per counter over ROWS rows, so cols = bytes / 4.

The floor of 64 columns is a backstop for callers outside config resolution, which rejects a cache.tinylfu.sketch_bytes small enough to reach it (decdn_common::config::MIN_TINYLFU_SKETCH_BYTES). It keeps the width above super::sketch::SHARDS, below which a sharded sketch degenerates to one column per shard (see ShardedCountMinSketch::new). It is not a width the estimates read usefully at: 64 columns over super::sketch::SHARDS shards is four columns per shard, and the collision rate that matters is the per-shard one.

Trait Implementations

impl Debug for TinyLfuEstimator

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl FrequencyEstimator for TinyLfuEstimator

fn observe(&self, hash: Hash)

Record one access to hash. The engine calls this on every serve.

fn estimate(&self, hash: Hash) -> u32

The current decayed access count for hash.