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preferred_node_order

aion_server::worker::placement_cache

Function preferred_node_order 

Source 
pub fn preferred_node_order(
    placement: &NamespacePlacement,
) -> Vec<Option<String>>
Expand description

The ordered node-filter tiers an UNPINNED row consults for the Prefer{L} two-tier spill (Control-Plane Phase 2, P2-P3) — the SINGLE source of the prefer-then-spill sequence shared by BOTH the gRPC (WorkerOutboxDispatch) and liminal (RegistryLiminalDispatch) dispatch paths, so the two transports can never diverge on what “prefer labelled worker, spill to any” means.

The returned sequence is a list of node filters to try IN ORDER, stopping at the first that has a live worker:

  • Prefer{L} → each label in L (deterministic BTreeSet order) as Some(label), then a final None spill tier (any live worker). An empty L collapses to just the None spill.
  • Unplaced → a single None tier (any live worker).

Pinned{L} is NOT dispatched through this fn: worker_selection_for routes it to the NON-spilling WorkerSelection::Required decision (require an L-labelled worker, WAIT on absence, never spill — P2-I1, #164). The Pinned arm here is only the internal fall-through of the soft Prefer path and never satisfies a hard pin.

This is consulted ONLY for an unpinned row (row.node == None): an authored Some(N) pin is authoritative and never enters this path. The result is a pure worker-SELECTION input; it never mutates the recorded row’s node (the determinism invariant, CP-Phase-2 §2.4).