[erlang-questions] WHOLETABLE lock on schema

[Hal Snyder]

I am seeing a stuck lock on the schema of a mnesia database. I'm not  
sure how it's happening yet. We run two nodes with disc_copies of the  
schema and several more with ram_copies of it, but I think all the  
nodes in question are listed in running_db_nodes.

Here is another way to create the lock. I don't think this is what is  
happening to the problem system above, but it would be nice to know  
if there is a good way to resolve the general problem without downtime:

N='some_fictional_node@REDACTED'.
mnesia:add_table_copy(schema, N, ram_copies).
mnesia:change_table_copy_type(schema, N, disc_copies).
mnesia:change_table_copy_type(schema, N, ram_copies).
-- at this point, erlang shell does not come back
-- you can interrupt it or remote in, though

Last line could probably be anything that wants to lock the schema.  
For example,
   mnesia:create_table(baz,[]).
does the same thing.

If you remote in from another node, you can do
   mnesia:system_info(held_locks).
and you will see something like this:
   [{{schema,'______WHOLETABLE_____'},write,{tid,5,<4163.81.0>}}]