Struct ShardedCountMinSketch 

pub struct ShardedCountMinSketch { /* private fields */ }

A CountMinSketch split into SHARDS independently locked pieces on one node-wide aging clock.

Every counter a given key touches lives in one shard, so an increment or an estimate takes exactly one shard lock and reads or writes ROWS counters. Halving is per shard and lazy: the shard is aged on its next touch by the number of node-wide windows that have elapsed since it last caught up. So the work is 1 / SHARDS of the array under one lock, while every counter is caught up to the node-wide clock at the moment it is read. A ranking pass reads each candidate separately, so it carries one halving of skew for every window boundary it crosses. A halving applied evenly across a pass cannot invert the ranking — it only creates ties — but candidates read on opposite sides of a boundary can misorder, and two whose estimates are within a factor of two can swap. The window is cols * 10 observations, so a sweep crossing even one boundary is already the uncommon case, and the next sweep re-reads both on one side of it.

The interior mutability is deliberate — the frequency estimator is shared by every serve completion and every fill-path admission read, so both take &self and neither can serialize on a single process-wide lock.

Implementations

impl ShardedCountMinSketch

pub fn new(cols: usize) -> Self

Build a sketch of cols total columns per row, spread over SHARDS shards. The per-shard width rounds up, so the realized total is at least cols.

A cols below SHARDS yields one shard per column, which is a degenerate sketch rather than a smaller one: at cols <= SHARDS every shard is one column wide, so all ROWS rows of a shard index the same counter and the min-over-rows stops discriminating between keys that share a shard. Callers wanting a small sketch should floor cols well above SHARDS, as super::tinylfu::TinyLfuEstimator::new does.

pub fn increment(&self, key: &Hash)

Count one sighting of key, locking only its shard.

A poisoned shard recovers its inner sketch: the counters are approximate popularity evidence, and refusing to count into a shard would silently freeze the frequency of every key routed to it.

pub fn estimate(&self, key: &Hash) -> u8

The count-min estimate for key, locking only its shard. An absent shard (only reachable from an empty sketch) reads as never seen.

Reading ages the shard too: a key in a shard that has seen no traffic for several windows must not read back at the value it held before those windows elapsed, or a cold key would outrank a warm one.

Trait Implementations

impl Debug for ShardedCountMinSketch

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

Formats the value using the given formatter.