[erlang-questions] Use of uuidgen with a mnesia application

[Anders Nygren]

On Fri, Jun 6, 2008 at 9:43 AM, Alexander Lamb
<alexander.lamb@REDACTED> wrote:
> Hello,
>
> I need to generate ids to be used as mnesia keys which will be unique
> not only withing a cluster of Erlang nodes but also globally (e.g. may
> be read from a Java program).
>
> I initially thought of writing my own uuidgen function, but it seems
> like reading the mac address of network interfaces can be rather
> cumbersom depending on systems.
>
> So I decided to use uuidgen from the system and convert it to binary
> (for efficiency).
>
> Is this the correct way of doing things:
>
> verify_guuid(Value) ->
>        A = lists:nth(9,Value),
>        B = lists:nth(14,Value),
>        C = lists:nth(19,Value),
>        case [A,B,C] of
>                "---" -> true;
>                _         -> false
>        end.
>
> make_guuid() ->
>        First = os:cmd("uuidgen -t"),
>        case verify_guuid(First) of
>                true    -> Result = First;
>                false   -> Second = os:cmd("uuidgen"),
>                                   case verify_guuid(Second) of
>                                                true  -> Result = Second;
>                                                false -> Result = "error",
>                                                                 throw({uuidgen_error,Second})
>                                   end
>        end,
>        erlang:list_to_binary(Result).
>
> Now, the reason I have this cascade of case is because on Linux (our
> Ubuntu servers) it recognizes the -t option to generate the uuid and
> on MacOSX (our dev machines) it does not.

Wouldn't it be "nicer" to use os:type/0 and os:version/0 to detect
what system You are running on?

/Anders

> Call me crazy, but I never feel confortable about using a totally
> random uuid to identity medical records that might be copied from
> system to system, exported, etc... even if the probability of
> collision is lower than that of a large asteroid hitting earth!
>
> What is your strategy for this (maybe this is a question to ask the
> couchdb developers, since they use guuids to identify the documents)?
>
> Thanks,
>
> Alex
> --
> Alexander Lamb
> Founding Associate
> RODANOTECH Sàrl
>
> 4 ch. de la Tour de Champel
> 1206 Geneva
> Switzerland
>
> Tel:  022 347 77 37
> Fax: 022 347 77 38
>
> http://www.rodanotech.ch
>
>
>
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