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PgRegistry 0.3+ replaced the Erlang :pg backend with a self-contained
Elixir port. This migrates stagehand off the old API:
- Replace :pg scope with a PgRegistry :stagehand scope
- Use PgRegistry.register/3 in init instead of :via tuples for cluster
group membership (producers and cron)
- Use local Registry names for producer addressing (consumer subscription)
- Replace :pg.monitor with PgRegistry.monitor/2 for join/leave events
- Replace get_members/2 with lookup/2 (returns [{pid, value}])
- Update tests for new API shapes
Follow the Elixir convention of module-style atoms for named processes (e.g. MyApp.Registry, MyApp.PubSub).
- Replace manual leader election in Cron with Highlander, which ensures a single cron process runs cluster-wide via :global - Remove cron's PgRegistry dependency entirely - Register cron in the local Registry for addressability - Rename PgRegistry scope from Stagehand.PgRegistry to Stagehand.ProducerRegistry since it is now only used for producer cluster discovery
Move PgRegistry scope startup from Stagehand.Supervisor (with idempotent case/match) to a proper Application module. The scope is now started once when the :stagehand application boots.
Producers are discovered cluster-wide via PgRegistry and addressed by pid (consumer subscribes via self(), router uses producers_for_queue). The local Registry name was unused. Producer still accepts an optional name: for direct unit tests.
Cron doesn't need a local name — it's a Highlander singleton found through :global. Test helper walks the Highlander supervision tree to find the cron pid.
Rendezvous (HRW) hashing needs only the member list and a key —
no separate ring structure to build and maintain. The implementation
is a single Enum.max_by over :erlang.phash2({node, key}).
Removes the libring dependency.
A pid's internal representation differs between the local node (where it shows as <0.N.C>) and remote nodes (where the first element is a node-specific identifier). Hashing on node(pid) ensures all nodes in the cluster compute the same winner for a given key.
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Summary
~> 0.2.2to~> 0.4:pgscope with a PgRegistry-managed:stagehandscopePgRegistry.register/3ininitinstead of:viatuplesRegistrynames for consumer subscription addressing:pg.monitor/2withPgRegistry.monitor/2for cluster join/leave eventsget_members/2withlookup/2(extracts pids from[{pid, value}])Test plan
mix test— 82 tests, 0 failures