CODEWITHSUNDEEP
erlangrpcmnesia
jasmad
jasmad

Reputation: 115

Creating cursor with erlang rpc with mnesia activity

Hi I'm trying to make a cursor in mnesia from a remote node, for example: I have the node which is the mnesia database owner and runs important processes in a dedicated server machine, and another node which have a process running in other computer and have to go through all the items to make some simple operations with the data. The thing is that I can make the miscellaneous process work if runs in the same node of mnesia but not remotely. This is my code that runs locally:

make_cursor_local() ->
  QD = qlc:sort(mnesia:table(customer, [{traverse, select}])),
  mnesia:activity(async_dirty, fun() -> qlc:cursor(QD) end, mnesia_frag).

get_next_local(Cursor) ->
  Get = fun() -> qlc:next_answers(Cursor,100) end,
  mnesia:activity(async_dirty, Get, mnesia_frag).

del_cursor_local(Cursor) ->
  qlc:delete_cursor(Cursor).

This is my actual code using rpc:

make_cursor() ->
  Sort = rpc:call(?NamespaceNode, mnesia, table, [customer, [{traverse, select}]]),
  QD = rpc:call(?NamespaceNode, qlc, sort, [Sort]),
  CursorCreation = fun() -> qlc:cursor(qlc:sort(Sort)) end,
  Cursor = rpc:call(?NamespaceNode, mnesia, activity, [async_dirty, CursorCreation, mnesia_frag]),
  Cursor.

get_next(Cursor) ->
  Get = fun() -> rpc:call(?NamespaceNode, qlc, next_answers, [Cursor, 100]) end,
  Next = rpc:call(?NamespaceNode, mnesia, activity, [async_dirty, Get, mnesia_frag]),
  Next.

del_cursor(Cursor) ->
  rpc:call(?NamespaceNode, qlc, delete_cursor, [Cursor]).

This code is generating this error making the mnesia activity call in the make_cursor function:

{badrpc,
       {'EXIT',
           {undef,
               [{#Fun<cleaner_app.2.116369932>,[],[]},
                {mnesia_tm,non_transaction,5,
                    [{file,"mnesia_tm.erl"},{line,738}]},
                {rpc,'-handle_call_call/6-fun-0-',5,
                    [{file,"rpc.erl"},{line,205}]}]}}}  {badrpc,{'EXIT',{undef,[{#Fun<misc_app.2.116369932>,[],
                     []},
                    {mnesia_tm,non_transaction,5,
                               [{file,"mnesia_tm.erl"},{line,738}]},
                    {rpc,'-handle_call_call/6-fun-0-',5,
                         [{file,"rpc.erl"},{line,205}]}]}}}

Upvotes: 1

Views: 215

Answers (1)

jasmad
jasmad

Reputation: 115

I found that the remote node can't execute anonymous functions created in another node so the error posted can be solved this way:

make_cursor() ->
   Sort = rpc:call(?NamespaceNode, mnesia, table, [customer, [{traverse, select}]]),
   QD = rpc:call(?NamespaceNode, qlc, sort, [Sort]),
   rpc:call(?NamespaceNode, mnesia, activity, [sync_transaction, fun qlc:cursor/1, [QD], mnesia_frag]).

I found the answer here what kind of types can be sent on an erlang message?

Now I have to solve the Cursor ownership because I cant execute it from the remote node.

This is the error:

{badrpc,
{'EXIT',
    {aborted,
        {not_cursor_owner,
            [{qlc,next_answers,
                 [{qlc_cursor,{<6920.991.0>,<6920.990.0>}},100],
                 [{file,"qlc.erl"},{line,515}]},
             {mnesia_tm,apply_fun,3,[{file,"mnesia_tm.erl"},{line,833}]},
             {mnesia_tm,execute_transaction,5,
                 [{file,"mnesia_tm.erl"},{line,813}]},
             {mnesia,wrap_trans,6,[{file,"mnesia.erl"},{line,394}]},
             {rpc,'-handle_call_call/6-fun-0-',5,
                 [{file,"rpc.erl"},{line,205}]}]}}}}

Upvotes: 0

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