mnesia_repl_and_frag2.erl

%% Sample for mnesia fragmentation with load balancing.

-module(mnesia_repl_and_frag2).

-compile([export_all]).

-record(store, {key, value}).

primary() ->
  net_kernel:start([localnode(1), longnames]),
  ok = mnesia:start(),
  ExtraNodes = lists:map(fun launch_node/1, extra_nodes()),
  Nodes = [node() | ExtraNodes],
  mnesia:change_config(extra_db_nodes, ExtraNodes),
  case mnesia:create_table(store,
                           [{record_name, store}, {type, set},
                            {frag_properties,
                             [{node_pool, Nodes},
                              {n_ram_copies, 2},
                              {n_fragments, 16}]},
                            {attributes, record_info(fields, store)}]) of
    {atomic, ok} ->
      add_data(1, 1000),
      {ok, created};
    {aborted, {already_exists,store}} ->
      {ok, already_exists};
    {aborted, _Reason} ->
      {aborted, _Reason}
  end.

cleanup() ->
  mnesia:delete_table(store),
  lists:map(fun stop_node/1, extra_nodes()),
  mnesia:stop().

extra_nodes() ->
  lists:seq(2, 5).

launch_node(Index) ->
  {ok, Node} = case slave:start_link('127.0.0.1', Index) of
                 {ok, Node2} -> {ok, Node2};
                 {error, {already_running, Node2}} -> {ok, Node2}
               end,
  ok = rpc:call(Node, mnesia, start, []),
  ok = rpc:call(Node, mnesia, wait_for_tables, [[schema], 1000]),
  Node.

stop_node(Index) ->
  slave:stop(localnode(Index)).

localnode(Index) ->
  list_to_atom(lists:flatten(io_lib:format("~B@127.0.0.1", [Index]))).

table_info(Item) ->
  mnesia:activity(async_dirty, fun mnesia:table_info/2,
                  [store, Item],
                  mnesia_frag).

add_data(Start, Stop) ->
  F = fun(Key) ->
          mnesia:activity(async_dirty, fun mnesia:write/3,
                          [store,
                           #store{key = Key, value = Key},
                          dirty_write],
                          mnesia_frag)
      end,
  lists:foreach(F, lists:seq(Start, Stop)),
  ok.