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transactionserlangnestedabortmnesia

Erlang Mnesia nested transaction aborted

i have the following code:

J = fun()->mnesia:clear_table(names) end.
 mnesia:activity(transaction, J, [], mnesia_frag).

and i get this error:

** exception exit: {aborted,{aborted,nested_transaction}}

i could just run 

mnesia:clear_table(names)

but since table name is fragmented over several nodes i thought i have to use mnesia_frag module.

what am i doing wrong ? and how would it be correct? Thank you.

Solution

  • you are correct that mnesia:clear_table(names) will not clear the entire fragmented table.

    mnesia:clear_table/1 already runs inside a transaction, so you can not use it with the mnesia:activity transaction AccessContext.

    instead try:

    mnesia:activity(sync_dirty, fun mnesia:clear_table/1, [names], mnesia_frag).

    if you look at the source code in mnesia_frag.erl, you'll see that it's just calling mnesia:clear_table/1 on each individual table. Assuming 4 frags, the above is basically equivalent to:

    [mnesia:clear_table(T) || T <- [names, names_frag2, names_frag3, names_frag4]].

    the table names coming from:

    mnesia_frag:frag_names(names).