What is mnesia:all_keys/1 used for?

mnesia:all_keys(Table) returns every primary key currently stored in a table, run inside a transaction (or a dirty context via mnesia:dirty_all_keys/1) — a quick way to enumerate a table's contents by key without writing a match specification.

mnesia:transaction(fun() ->
    mnesia:all_keys(person)
end).
%% -> {atomic, [1, 2, 3, 4]}

It's convenient for small-to-moderate tables (iterating configuration, listing registered sessions), but it does mean scanning the whole table's key space, so on a very large table a more targeted select/2 query with an actual filter condition is usually a better fit than pulling every key and filtering client-side afterward.

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