[erlang-questions] mnesia fallbacks with local_content

Håkan Mattsson <>
Thu Jan 9 14:05:39 CET 2014


Hmm, it did not work as I expected. I encountered a bug in
mnesia_checkpoint:select_writers/2. Currently it does not handle
local_content tables properly. The bug implies that the local backup
on the remote nodes does not include local_content tables at all.
Anyone that want to do a contribution?

/Håkan

On Thu, Jan 9, 2014 at 1:51 PM, Håkan Mattsson <> wrote:
> It is a bit complicated and partly undocumented. You need to do it in
> several steps:
>
> 1. Activate a global checkpoint (mnesia:activate_checkpoint/1).
> 2. Perform a local backup on each node (mnesia:backup_checkpoint/3)
> 3. Dectivate the checkpoint (mnesia:deactivate_checkpoint/1)
> 4. Install a local fallback (from the local backup) on each node
>     (mnesia:install_fallback/2)
>
> See mnesia_log:check_backup_arg_type/2 for details of the third
> (partly undocumented) argument of mnesia:backup_checkpoint/3.
>
> /Håkan
>
> On Wed, Jan 8, 2014 at 7:48 PM, Anders Nygren <> wrote:
>> I am trying to figure out if it is possible to use mnesia fallbacks with
>> tables with local_content. The documentation does not provide much
>> information on this and my experiments seems to imply that it is not
>> possible.
>>
>> Running erlang 5.9.1, mnesia 4.7, I have two nodes A and B.
>>
>> I have a table t1, that has {local_content, true},
>> If I take a backup on node A and install that as a fallback and then restart
>> mnesia, the content of table t1 on node B gets replaced with the contents
>> from t1 on node A.
>>
>> Is there any way to get this to work, i.e. to get the local contents
>> restored correctly on all nodes from a fallback?
>>
>> /Anders
>>
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