Enum BandwidthClass 

pub enum BandwidthClass {
    Foreground,
    Background,
    Realtime,
}

Per-stream bandwidth class hint. Drives the v0.3 Phase D admission gate (BandwidthBudget::try_consume_with_class) + the anti-starvation hatch.

Foreground is the default — interactive workloads, normal RPC responses, anything a person is waiting on.

Background is admitted only when the bucket has at least (1 - background_fraction) × capacity available. The anti-starvation hatch one-shot-bypasses the gate when Background has been denied for > 60 s.

Realtime bypasses the rate-limit failure path entirely (still subject to disk-pressure circuit-breakers). Reserved for control-plane traffic and operator-triggered repair sweeps.

Variants

Foreground

Default class — interactive / user-driven work.

WARNING: v0.2-compat default — silently slips past D-phase rate bounds. This is Default so existing v0.2 callers migrating to v0.3 preserve their pre-D2 latency characteristics: every replication request keeps acting like Foreground unless the caller explicitly tags Background or Realtime. The trade-off is that a Phase-D-aware peer that FORGETS to override the default also gets full Foreground rate, undermining the budget bound. Code that emits or constructs SyncRequest / RuntimeInputs SHOULD pick a class explicitly per workload, not rely on Default.

Background

TB-scale background work — backfills, migrations, cold-blob warming. Bounded by background_fraction.

Realtime

Operator-pinned. Bypasses per-class rate budget.

Implementations

impl BandwidthClass

pub const FOREGROUND_WIRE: u8 = 0

Wire-encoded discriminant. Pinned for backward compat: new variants must take new discriminant values; never re-purpose an existing value. Wrapping a legacy peer’s missing-class trailing byte defaults to Foreground via Self::from_wire_or_default.

pub const BACKGROUND_WIRE: u8 = 1

See Self::FOREGROUND_WIRE.

pub const REALTIME_WIRE: u8 = 2

See Self::FOREGROUND_WIRE.

pub fn as_u8(self) -> u8

Encode to the 1-byte wire form. The replication layer appends this to SyncRequest frames as a trailing byte; legacy 55-byte frames omit it entirely and are read back via Self::from_wire_or_default.

pub fn from_wire_or_default(byte: u8) -> Self

Decode from the 1-byte wire form. Unknown discriminants (a forward-compat scenario where a future variant lands before this reader knows about it) decode as Foreground — conservative degrade that keeps unknown-class requests admitted under the most permissive gate rather than silently dropped.

Trait Implementations

impl Clone for BandwidthClass

fn clone(&self) -> BandwidthClass

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for BandwidthClass

impl Debug for BandwidthClass

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

Formats the value using the given formatter.

impl Default for BandwidthClass

fn default() -> BandwidthClass

Returns the “default value” for a type.

impl Eq for BandwidthClass

impl Hash for BandwidthClass

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for BandwidthClass

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

Tests for self and other values to be equal, and is used by ==.

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

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl StructuralPartialEq for BandwidthClass