What is a Mnesia transaction?

A Mnesia transaction wraps a set of reads and writes so they either all succeed together or none of them take effect — the same all-or-nothing guarantee a traditional database transaction provides, implemented here across Erlang processes and, if the table is replicated, across nodes.

mnesia:transaction(fun() ->
    mnesia:write(#person{id = 1, name = "Ada", age = 34}),
    mnesia:write(#person{id = 2, name = "Grace", age = 41})
end).

The function passed to mnesia:transaction/1 runs with automatic locking and rollback: if any operation inside it fails (a conflict, an exception), Mnesia aborts the whole transaction and none of the writes are applied. This is the safe, default way to interact with Mnesia data, and is what you should reach for unless you have a specific reason to use faster, less safe "dirty" operations instead.

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