[erlang-questions] Unable to create Mnesia table

[Youngkin, Rich]

Just in case it's helpful to anyone... I've discovered the error of my ways
(but I'm still looking towards a solution). This application used to start
Mnesia directly after creating the schema (only on the initial startup of
course). When creating the release I changed this by adding the mnesia
application to the {applications, [...]} tuple in the app.src file. I did
this to fix another problem caused by the Mnesia beam files not being
included as part of the Erlang distro created by relx.  So in the release
version, Mnesia is up and running before the schema is created. So I end up
with a started Mnesia application without a schema, which of course is
needed to define tables.

So now on the my next question, how can I get the schema initialized if
Mnesia is started prior to schema creation?  Some guy who gives crappy
answers  :) had this post in StackOverflow that gave a partial answer -
http://stackoverflow.com/questions/14083367/mnesia-doesnt-restart-with-supervisor.
Is this really the preferred way of doing this? Seems like a bit of a hack
to me (but I'm still a newbie, what do I know :>).

Cheers,
Rich

On Wed, Oct 8, 2014 at 8:33 AM, Youngkin, Rich <richard.youngkin@REDACTED
> wrote:

> Hi all,
>
> I recently converted an existing application to a release using relx.
> After that the application isn't able to create any Mnesia tables. I can't
> reproduce the problem in the Erlang shell (except by creating the table
> before creating the schema). This is confusing because the app code creates
> the schema prior to creating the table.
>
> Here is the error:
> 12:20:18.929 [info] Creating a new schema from scratch...
> 12:20:18.929 [info] Mnesia started, creating tables...
> 12:20:18.929 [info] Attempting to create table with TableDef
> {pe_properties,{disc_copies,[{attributes,[key,value]},{record_name,pe_kvpair}]}}
> 12:20:18.931 [error] gen_server pe_membership terminated with reason: bad
> return value:
> {error,{unable_to_init_schema,{aborted,{bad_type,pe_properties,disc_copies,'
> prospero@REDACTED'}}}}
>
>
> Here's the associated application code:
>
>       error_logger:info_msg("Creating a new schema from scratch...~n"),
>
>       %% TODO: TEMP WORKAROUND TO DEBUG MNESIA SCHEMA CREATION PROBLEM
>
>       application:set_env(mnesia, dir, "/var/data/prospero"),
>
>       mnesia:create_schema([node()]),
>
>       mnesia:start(),
>
>       error_logger:info_msg("Mnesia started, creating tables...", []),
>
>       case create_tables(pe_migrate:get_schema()) of
>
>
> The line application:set_env(...) was added in case the Mnesia directory
> wasn't getting created properly due to the move to a relx-built release. I
> had a similar entry in vm.args that I may have gotten wrong (-mnesia dir
> '"/var/data/prospero"'). Interestingly enough, I don't see any artifacts
> associated with the schema creation in the Mnesia dir (e.g., schema.DAT).
> I'm wondering if this is a clue as to what the cause is.
>
> pe_migrate:get_schema()) returns a list of TableDefs. create_tables
> iterates through that list creating the tables one at a time. The failure
> occurs when attempting to create the first table.
>
> Thanks, Rich
>
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