[erlang-questions] backing up mnesia ram_copies tables

Dan Gudmundsson <>
Thu Dec 13 13:10:33 CET 2012


It is the way it is intended.
If you create your own checkpoint you can specify what you want to be
included in the backup.
/Dan


On Thu, Dec 13, 2012 at 12:36 PM, Philip Clarke <>wrote:

> Hi,
>
> Should it be possible to make a backup of tables in mnesia if you just
> have ram_copies ?
>
> The documentation at http://www.erlang.org/doc/man/mnesia.html#backup-1 does
> not seem to imply that there is any such limitation.
>
> However when I examine the backup file created from mnesia:backup/1 it
> does not seem to have any table data.
>
> I use this simple test to check the backup.  It will fail
> with {aborted,{no_exists,bup_rec,all}}.
>
>
> -record(bup_rec, {key, val}).
>
> test_cannot_restore_backup() ->
>     Node = node(),
>     mnesia:lkill(),
>     ok = mnesia:delete_schema([Node]),
>     mnesia:start(),
>     mnesia:wait_for_tables([schema], infinity),
>
>     OldBup = "old.BUP",
>     file:delete(OldBup),
>
>     CreateList = [{ram_copies, [Node]},
>                   {attributes, record_info(fields, bup_rec)}],
>     {atomic, ok} = mnesia:create_table(bup_rec, CreateList),
>     mnesia:wait_for_tables([bup_rec], infinity),
>     OldRecs = [#bup_rec{key = I, val = I * I} || I <- lists:seq(1, 10)],
>     lists:foreach(fun(R) -> ok = mnesia:dirty_write(R) end, OldRecs),
>
>     mnesia:backup(OldBup),
>
>     mnesia:stop(),
>     ok = mnesia:delete_schema([Node]),
>     mnesia:start(),
>     mnesia:wait_for_tables([schema], infinity),
>
>     mnesia:restore(OldBup, [{default_op, recreate_tables}]),
>     ok = mnesia:table_info(bup_rec, all).
>
>
> I would like to know if I am doing the backup wrong, or if this is
> something which is not supported.
>
> Thanks
> Philip
>
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