mnesia_tablewise_backup.erl

%Copy and paste the below Anonymous functions to Erlang Shell
Get_table_structure = fun(TableName) -> 
	{tables,[{TableName,[{record_name,mnesia:table_info(TableName,record_name)},{attributes,mnesia:table_info(TableName,attributes)}]}]}
end.

Read_tablerows = fun(Rows,TableName,IODevice,Key) ->
	lists:foldl(fun(_,Acc) ->
		NextKey = mnesia:dirty_next(TableName,Acc),
		[Record] = mnesia:dirty_read(TableName,Acc),	
		io:format(IODevice,"~p.~n",[Record]),
		NextKey
	end, Key, lists:seq(1,Rows))	
end.

Write_table_to_file = fun(TableName,NumberOfRowsToBackup,IODevice) ->
	FirstKey = mnesia:dirty_first(TableName),
	Read_tablerows(NumberOfRowsToBackup,TableName,IODevice,FirstKey)
end.

Write_fulltable_to_file = fun(TableName,IODevice)	->
	TableData = ets:tab2list(TableName),
	lists:foreach(fun(Record) -> 
			io:format(IODevice,"~p.~n",[Record])
			end ,TableData),
	file:close(IODevice)
end.

%Call this function with the number of rows you want to backup. 
%Here Due to memory issues in my dev machine I am keeping the number to 5000 rows max.
Backup_Table = fun(TableName,NumberOfRowsToBackup) -> 
	GetTableStructure = Get_table_structure(TableName),
	Path = lists:concat(["/tmp/",erlang:atom_to_list(TableName),".bak"]),
	case file:open(Path,[write]) of
		{ok,IODevice} -> 
			io:format(IODevice,"~p.~n",[GetTableStructure]),
			case NumberOfRowsToBackup > 5000 of
				true -> Write_table_to_file(TableName,NumberOfRowsToBackup,IODevice);
				false -> Write_fulltable_to_file(TableName,IODevice)
			end;
		{error,Reason} -> 
			io:format("Error Occured due to ~p~n",[Reason])
	end
end.

%Use this Below command to save all mnesia tables in text format. All the files are available in /tmp/ with table_name.bak 
%lists:foreach(fun(X) -> TableSize = mnesia:table_info(X,size), Backup_Table(X, case TableSize > 5000 of true -> 5001; false -> 0 end) end,mnesia:system_info(tables)).

%use mnesia:load_textfile(Path) to load the table into another machine
%If you want to backup them as it is.
%lists:foreach(fun(X) -> Path = lists:concat([PATH,erlang:atom_to_list(X),".bak"]), mnesia:load_textfile(Path) end,mnesia:system_info(tables)).