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LocalAI/docs/content/features
Ettore Di Giacinto 49128cf486 feat(distributed): keep the listener draining and let it come back
PostgreSQL holds undelivered notifications in a queue it shares with every
session on the server, and it kills a listener that stops draining. Two failure
modes follow, and both are silent: a carrier that blocked on a slow resolver
would lose its connection and with it every later broadcast, and a carrier that
reconnected without re-registering would be connected and deaf.

The receive and dispatch halves were already separate. What was missing is
everything around them. The listener path moves into listener.go and gains a
carrier-level Dropped() so a replica that is behind can be seen; the queue depth
and the spill retention become Config fields with exported defaults; the LISTEN
session gets an application_name so an operator can count listeners in
pg_stat_activity and a spec can drop exactly one of them; and OnReconnect fires
after the re-LISTEN, on a goroutine of its own, because a callback re-hydrates
from a database and must never run on the path whose only job is to drain.

That callback is reached through an optional interface assertion, so deleting
its invocation compiles and every adopter silently stops converging. The spec is
the only guard, and it is named in a comment at the site.

The slow consumer is proved through the transport rather than a seam: an ACCESS
EXCLUSIVE lock on bus_messages stalls the resolver's spill SELECT for exactly as
long as the spec holds it, and the listener is shown still draining and dropping
while it does. The dropped connection is a pg_terminate_backend matched on the
carrier's own application name.

Neither Dropped nor IsConnected is on messaging.Broadcaster, and a spec asserts
that over the interface type. Both are facts about a frontend; the conditions a
scheduler acts on are facts about a worker, and no consumer holding the
interface can read one as the other.

Assisted-by: Claude Opus 5 [claude-code]
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
2026-09-03 10:23:40 +00:00
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