Function compile 

pub fn compile(
    relation: &AudioRelation,
    session_of: &BTreeMap<ConnectionId, SessionId>,
    since: &BTreeMap<SessionId, u64>,
    silence: &Silence,
) -> AudioRouting

Compile the declared relation into the table the voice plane reads.

session_of resolves a connection to the session it is rendered under. Connections with no rendered user are dropped from the table: a sender nobody can see is a sender whose audio the client would discard (guide 1.2), and a receiver with no session has nothing to deliver to.

since carries the version each session first appeared at, threaded through from the shard so it survives recompilation.

silence removes muted senders and deafened receivers before any route is written down, rather than after: a muted speaker in a domain of fifty costs nothing at all here, where filtering the finished table would cost the fifty routes it should never have had.

Cost

The compiled table is quadratic in a domain’s size by construction: a full mesh of M members really does have M·(M-1) directed routes, and no representation of an adjacency list avoids writing them down. What this avoids is doing so through an ordered set: the members are resolved once per domain and the receiver lists are appended to directly, so the cost is a quadratic number of Vec pushes rather than of tree insertions. That is the difference between microseconds and tens of milliseconds at 500 connections.