Question

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.

Answer 1

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).