[erlang-questions] WHOLETABLE lock on schema

Hal Snyder <>
Wed May 23 17:58:04 CEST 2007

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:

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,
does the same thing.

If you remote in from another node, you can do
and you will see something like this:

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