Struct ShuffleSharding 

pub struct ShuffleSharding {
    pub percent: u32,
    pub min_backends: u32,
    pub mode: ShardMode,
}

A cluster’s shuffle-sharding policy (sozu-proxy/sozu#524).

Shuffle sharding (Colm MacCárthaigh, Workload isolation using shuffle sharding, Amazon Builders’ Library, 2019) gives each client a shard: a small subset of the cluster’s backends, drawn so that two clients rarely share all of theirs. A client that overloads or poisons its shard then takes down only the clients whose shard is entirely inside its own. With N backends in shards of k there are C(N, k) shards, against N / k with plain partitioning: C(8, 2) = 28 against 4.

Here a client’s shard is the top k of the rendezvous (HRW) ranking of its affinity key over the cluster’s primary backends (hrw_score; David Thaler and Chinya Ravishankar, Using name-based mappings to increase hit rates, IEEE/ACM Transactions on Networking, 1998). That makes a shard stable: removing a backend outside a client’s shard leaves the shard unchanged, and adding one can only displace the shard’s lowest-ranked member, so a change of N moves clients only at the tail of their ranking. The cluster’s load-balancing policy then selects inside the shard.

Fields

percent: u32

Share of the primary backends in a shard, 1..=100.

min_backends: u32

Sharding applies only from this many primary backends.

mode: ShardMode

What an exhausted shard does.

Implementations

impl ShuffleSharding

pub fn from_cluster( shard_percent: Option<u32>, shard_min_backends: Option<u32>, shard_mode: Option<i32>, ) -> Option<Self>

The sharding a cluster configures, None when shard_percent is unset. shard_min_backends defaults to DEFAULT_SHARD_MIN_BACKENDS, shard_mode to FALLBACK.

pub fn shard_size(&self, primaries: usize) -> Option<usize>

The shard size k for a cluster of primaries primary backends: max(2, ceil(percent × primaries / 100)), capped at primaries. None below min_backends, where the cluster is not sharded.

Trait Implementations

impl Clone for ShuffleSharding

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for ShuffleSharding

impl Debug for ShuffleSharding

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

Formats the value using the given formatter.

impl Eq for ShuffleSharding

impl PartialEq for ShuffleSharding

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for ShuffleSharding