[erlang-questions] how: mnesia with simultaneous permanent node failure (EC2)

[Dan Gudmundsson]

You should be able to start an old node with a clean directory and 
connect it mnesia:change_config(extra_db_nodes, [OneOfYourNodes]) so it 
will download the schema and and convert it disc, and the other tables 
from the other nodes.

/Dan

Scott Lystig Fritchie wrote:
>>>>>> "pm" == Paul Mineiro <paul-trapexit@REDACTED> writes:
> 
> pm> however when i tried to apply the procedure to simultaneous loss
> pm> of two nodes, i ran into a problem; calling
> pm> mnesia:del_table_copy/2 of schema requires all other nodes to be
> pm> active, and is this scenario i have lost two nodes simultaneously
> pm> (attached as test-disaster-two).
> 
> Yup, I've also discovered that feature.  Heh, some colleagues have run
> into problems when they've intentionally created such a failure via
> the "rm -rf" trick.  I had to explain that just because node C in a
> cluster lost it's mind doesn't mean that A & B & others haven't
> forgotten that C is a member.
> 
> My solution was to create a backup of each node after a schema change,
> and use that backup to bootstrap a dead node back to life ... then use
> mnesia:del_table_copy() if I really wanted to remove that node from
> the cluster.
> 
> An interesting experiment that I haven't tried ... Mnesia backups, by
> default, include all tuples from all tables.  Either by using a custom
> backup module, or by post-processing a backup via
> mnesia:traverse_backup(), to include only the schema table.  I wonder
> if restoring only the schema table on each formerly-dead node is
> sufficient?
> 
> -Scott
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