[erlang-questions] Mnesia: inconsistent views without netsplit?

[Daniel Dormont]

On Wed, Apr 27, 2016 at 3:03 AM, Dan Gudmundsson <dangud@REDACTED> wrote:
> 1) No clue. But would be interested if you have an idea what have gone
> wrong.
>
> 2) mnesia:del_table_copy(...) followed by mnesia:add_table_copy(..) should
> re-copy the table from the other nodes.

Thanks. I'll give that a try.

Along the same lines I was wondering: is there a setting I can use to
adjust the sensitivity of the system's detection of node disconnects,
either generically or specifically within Mnesia? My production
environment appears to have occasional momentary network hiccups (it's
Amazon EC2 instances spanning zones within a region, for anyone
curious). I'd like to make it less likely for those hiccups to cause
Mnesia to enter an inconsistent state, even if it means real failures
take a little longer to detect.

thanks,
Dan


>
> On Tue, Apr 26, 2016 at 9:30 PM Daniel Dormont <dan@REDACTED>
> wrote:
>>
>> Hi all,
>>
>> I have a three node Mnesia cluster (hosting a somewhat outdated
>> version of ejabberd, but I'm not sure that matters). I have a table
>> that is stored as ram_copies on all three nodes. Yet, this table has
>> differing numbers of records among the three.
>>
>> The table info from one of them is pasted below. Running the same
>> query on one of my other nodes, I get more or less the same result,
>> but the "size" is very different: 553 vs 867. And indeed, there are
>> individual records that turn up in a mnesia:read/2 or
>> mnesia:dirty_read/2 on one node and not the other.
>>
>> Yet, nothing in my log indicates that there was ever a netsplit or
>> disconnection. So I have two questions:
>>
>> 1) What might cause this? and
>> 2) Is there any way, especially given I know which records are
>> affected, to force some kind of replication on this table without
>> completely restarting one of the nodes?
>>
>> thanks,
>> Dan Dormont
>>
>>
>> [{access_mode,read_write},
>>  {active_replicas,['ejabberd@REDACTED',
>>                    'ejabberd@REDACTED',
>>                    'ejabberd@REDACTED']},
>>  {all_nodes,['ejabberd@REDACTED',
>>              'ejabberd@REDACTED',
>>              'ejabberd@REDACTED']},
>>  {arity,3},
>>  {attributes,[name_host,pid]},
>>  {checkpoints,[]},
>>  {commit_work,[]},
>>  {cookie,{{1341,344810,207763},'ejabberd@REDACTED'}},
>>  {cstruct,{cstruct,muc_online_room,set,
>>                    ['ejabberd@REDACTED',
>>                     'ejabberd@REDACTED',
>>                     'ejabberd@REDACTED'],
>>                    [],[],0,read_write,false,[],[],false,muc_online_room,
>>                    [name_host,pid],
>>                    [],[],[],{...},...}},
>>  {disc_copies,[]},
>>  {disc_only_copies,[]},
>>  {frag_properties,[]},
>>  {index,[]},
>>  {load_by_force,false},
>>  {load_node,'ejabberd@REDACTED'},
>>  {load_order,0},
>>  {load_reason,{active_remote,'ejabberd@REDACTED'}},
>>  {local_content,false},
>>  {majority,false},
>>  {master_nodes,[]},
>>  {memory,73643},
>>  {ram_copies,['ejabberd@REDACTED',
>>               'ejabberd@REDACTED',
>>               'ejabberd@REDACTED']},
>>  {record_name,muc_online_room},
>>  {record_validation,{muc_online_room,3,set}},
>>  {type,set},
>>  {size,867},
>>  {snmp,[]},
>>  {storage_properties,...},
>>  {...}|...]
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