Moving mnesia schema to another node

[Chandrashekhar Mullaparthi]

Look in the Mnesia user guide in Section 6.9.1

The following example illustrates how mnesia:traverse_backup can be used to
rename a db_node in a backup file: 

change_node_name(Mod, From, To, Source, Target) ->
    Switch =
        fun(Node) when Node == From -> To;
           (Node) when Node == To -> throw({error, already_exists});
           (Node) -> Node
        end,
    Convert =
        fun({schema, db_nodes, Nodes}, Acc) ->
                {[{schema, db_nodes, lists:map(Switch,Nodes)}], Acc};
           ({schema, version, Version}, Acc) ->
                {[{schema, version, Version}], Acc};
           ({schema, cookie, Cookie}, Acc) ->
                {[{schema, cookie, Cookie}], Acc};
           ({schema, Tab, CreateList}, Acc) ->
                Keys = [ram_copies, disc_copies, disc_only_copies],
                OptSwitch =
                    fun({Key, Val}) ->
                            case lists:member(Key, Keys) of
                                true -> {Key, lists:map(Switch, Val)};
                                false-> {Key, Val}
                            end
                    end,
                {[{schema, Tab, lists:map(OptSwitch, CreateList)}], Acc};
           (Other, Acc) ->
                {[Other], Acc}
        end,
    mnesia:traverse_backup(Source, Mod, Target, Mod, Convert, switched).

view(Source, Mod) ->
    View = fun(Item, Acc) ->
                   io:format("~p.~n",[Item]),
                   {[Item], Acc + 1}
           end,
    mnesia:traverse_backup(Source, Mod, dummy, read_only, View, 0).

cheers,
Chandru

> -----Original Message-----
> From: Erik Pearson [mailto:erik@REDACTED]
> Sent: 25 December 2001 02:19
> To: erlang-questions@REDACTED
> Subject: Moving mnesia schema to another node
> 
> 
> Hi,
> 
> I need to move a mnesia database from one node to another, 
> and haven't been 
> able to figure out how. Mnesia is okay if you move it around 
> on the same 
> machine (different directories), but doesn't like to be moved 
> to another 
> machine -- (e.g. tar it up and untar it somehwere else) -- 
> even if the 
> database directory is accessed via a generic directory name 
> through an 
> explicit -mnesia dir 'dirname' or -config configfile.
> 
> I've also tried restoring from a backup, but stopped that 
> after it ate up 
> all CPU on the server. I also tried using install_fallback, 
> but mnesia 
> complains with
> 
> {"No disc resident schema on local node", [myoldnode]}
> 
> The backup seems to keep a reference to the old node, and 
> doens't like to 
> be restored anywhere else...
> 
> Does anyone know how to do a "redirected backup and restore" 
> from one node 
> to another?
> 
> Thanks,
> 
> Erik Pearson
> 



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