Struct HllSketch 

pub struct HllSketch { /* private fields */ }

Minimal HyperLogLog sketch for approximate distinct counting.

Uses 2^precision registers. Default precision is 8 (256 registers, ~256 bytes of memory, ~2% standard error).

Wire Format

[precision: u8][registers: u8 * (2^precision)]

Implementations

impl HllSketch

pub fn new() -> Self

Create a new empty sketch with default precision (8).

pub fn with_precision(precision: u8) -> Self

Create a new empty sketch with the given precision.

Allocates 2^precision registers.

Panics

Panics if precision is not in the range 4..=18.

pub fn add_hash(&mut self, hash: u64)

Add a pre-hashed 64-bit value to the sketch.

pub fn merge(&mut self, other: &Self)

Merge another sketch into this one (HLL union).

Panics

Panics if the two sketches have different precisions.

pub fn estimate(&self) -> f64

Estimate the cardinality (number of distinct elements).

pub fn to_bytes(&self) -> Vec<u8>

Serialize the sketch to bytes.

pub fn from_bytes(bytes: &[u8]) -> Result<Self, TwoPhaseError>

Deserialize a sketch from bytes.

Errors

Returns TwoPhaseError::Serde if the bytes are malformed.

pub fn num_registers(&self) -> usize

Number of registers (2^precision).

pub fn precision(&self) -> u8

Precision (log2 of register count).

Trait Implementations

impl Clone for HllSketch

fn clone(&self) -> HllSketch

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for HllSketch

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

Formats the value using the given formatter.

impl Default for HllSketch

fn default() -> Self

Returns the “default value” for a type.