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Erlang / Erlang Advanced Interview questions

What is the pg (process groups) module used for?

pg lets multiple processes join a named group, cluster-wide, so a caller can broadcast or fan out work to every member without tracking individual PIDs itself — unlike global, which maps one name to exactly one process, pg maps one name to a set of processes.

pg:join(chat_room_42, self()),
Members = pg:get_members(chat_room_42),
[Pid ! {new_message, Msg} || Pid <- Members].

Typical uses include pub/sub-style fan-out (every subscriber process in a group gets a copy of an event) and worker pools where any member can pick up a task. It's deliberately simpler than global: it makes no attempt at strong consistency guarantees during partitions, favoring availability and low overhead, which fits well for use cases like broadcast messaging where an occasional stale group view is tolerable.

What is the key structural difference between pg and global?
What kind of use case does pg fit well?

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