What is a Mnesia node?

In Mnesia's context, a "node" is simply an Erlang node (a running BEAM instance with a name) that participates in a Mnesia database, either holding copies of tables directly or just being schema-aware of the cluster. A single logical Mnesia database can span several such nodes, all coordinating table replication and transactions between them.

mnesia:create_schema([nodea@host1, nodeb@host2]),
mnesia:create_table(person,
    [{disc_copies, [nodea@host1, nodeb@host2]},
     {attributes, [id, name, age]}]).

Which nodes hold a copy of a given table is decided per-table via the storage type options (ram_copies, disc_copies, disc_only_copies), and a node doesn't need to hold every table in the schema — you can have some nodes replicate only a subset of tables relevant to their role, while still being part of the same overall Mnesia cluster.

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