Trait PlacementSignals 

pub trait PlacementSignals {
    // Required methods
    fn member_capacity(&self, member: &NodeIdentity) -> MemberCapacity;
    fn range_load(
        &self,
        collection: &CollectionId,
        range_id: RangeId,
    ) -> RangeLoad;

    // Provided method
    fn member_attribute(
        &self,
        _member: &NodeIdentity,
        _key: &str,
    ) -> Option<&str> { ... }
}

The live cluster state the planner reads but does not own: each member’s advertised capacity and each range’s bytes/traffic.

Production backs this onto the disk-usage reporter and the per-range traffic counters; tests back it onto a scripted fake. Keeping it behind a trait is what makes the planner a pure policy.

Required Methods

fn member_capacity(&self, member: &NodeIdentity) -> MemberCapacity

The capacity member currently advertises. A member that advertises nothing (or is unknown) should report a zero-disk MemberCapacity, which makes it un-placeable rather than a div-by-zero hazard.

fn range_load(&self, collection: &CollectionId, range_id: RangeId) -> RangeLoad

The current load on (collection, range_id) — its bytes and its recent read/write traffic.

Provided Methods

fn member_attribute(&self, _member: &NodeIdentity, _key: &str) -> Option<&str>

Placement attribute advertised by member, such as a zone or region. Implementations that do not track topology attributes can leave this absent; spread rules then degrade through operator warnings instead of inventing topology.

Dyn Compatibility

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors