[erlang-questions] Mnesia folder

Peter J Etheridge petergi@REDACTED
Sat Jul 13 09:07:51 CEST 2019

Dear Daniel, 

Noticing references in the manual without explanation, I had spent
quite some time on search engines trying to understand nonode@REDACTED
It is starting to make sense now i have read your answer
Thank you, Daniel !
Happy coding,Peter

----- Original Message -----
From: "Dániel Szoboszlay" 
To:"Peter J Etheridge" 
Sent:Thu, 11 Jul 2019 23:30:44 +0200
Subject:Re: [erlang-questions] Mnesia folder

This directory was created because you once called
mnesia:create_schema/1 on a node called nonode@REDACTED (that is, on a
non-distributed node).
By the way, nonode@REDACTED is not really an error, per se. Every
Erlang node has a name (see erlang:node/0 [1]). For distributed nodes
the name is important, because other nodes can find and connect to it
via its name. But there can be non-distributed nodes too. They don't
listen to incoming connections and don't attempt to connect to other
nodes either. So their name is completely irrelevant, and by
definition they are always called nonode@REDACTED (It is also possible
to stop [2] and start [3] distribution on a node without stopping it.
If you do so, it will change its name.)
Now, the documentation sometimes calls nodes where distribution is
running "_alive_, and nodes where it is stopped "_not alive"_ These
names may be a bit confusing. A "not alive" node is still alive in the
sense that it is running and executing code. It is just not accessible
to other nodes via the Erlang distribution protocol.
Back to Mnesia: Mnesia allows you to create a distributed database,
but it can work perfectly on a single node as well. So it's even valid
to use Mnesia on a non-distributed node. If you do so, you will get
the directory you found. Of course, if you no longer want to use
non-distributed nodes and don't need this DB instance, you can just
delete it now.
On Thu, 11 Jul 2019 at 07:39, Peter J Etheridge  wrote:
dear list,having recently discovered that nonode@REDACTED is an error, i
now find a folder;
containing files;
could this be because i did not name my node?
thank you in advance,peter

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[1] http://erlang.org/doc/man/erlang.html#node-0
[2] http://erlang.org/doc/man/net_kernel.html#stop-0
[3] http://erlang.org/doc/man/net_kernel.html#start-1
[4] mailto:petergi@REDACTED
[5] mailto:erlang-questions@REDACTED
[6] http://erlang.org/mailman/listinfo/erlang-questions

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