[erlang-questions] Mnesia vs When Databases Lie: Consistency vs Availability in Distributed Systems

PatrickErj <>
Mon Dec 17 15:07:47 CET 2007


Ulf could you pls. find where the info on that page vanished. :)



Ulf Wiger (TN/EAB) wrote:
> 
> 
> Ok, I only browsed the article with half an eye, so I
> may be firing prematurely, but...
> 
> If you look at mnesia_frag, it allows you to exercise some
> control over the distribution of objects into fragments.
> 
> If you have a structured key {Continent, ...}, you could
> select a fragment from a subset of fragments on the
> right continent. These fragments could be replicated
> "intra-continentally", and you could perhaps guard against
> someone diving down to the bottom of the Atlantic and
> cutting the Transatlantic link, by implementing geographical
> redundancy (asynchronously logging events to a backup
> store on another continent.)
> 
> BTW, there is an old slide kit, called Mnesia Internals.
> It's supposed to be available here:
> 
> http://www.erlang-projects.org/Public/projects/erlangotp/mnesia_internals_sli/view
> 
> but I'm getting a "Bad Gateway" error at the moment.
> 
> BR,
> Ulf W
> 
> Joel Reymont skrev:
>> How does Erlang change or improve this situation?
>> 
>> http://tinyurl.com/2745ha
>> 
>> I can't imagine a fragmented Mnesia table would help here, not when  
>> one chunk lives in Europe and another in the US.
>> 
>> I also imagine there would be significant costs in Transatlantic  
>> replication (in terms of transaction time, not dollars) if a regular  
>> distributed Mnesia table is used.
>> 
>> I want to dig deep into Mnesia for the corresponding chapter of my  
>> book. I plan to try to figure out and write up the distributed commit  
>> protocol, for example.
>> 
>> I think I'll also try to set up exactly the scenario that the above  
>> article describes (two machines, multiple Mnesia nodes) and simulate  
>> denial of service attacks, tripping over power cords, etc.
>> 
>> I want to know exactly how much network bandwidth is taken by  
>> replication among other things and what exactly happens when I bring  
>> up a Mnesia node that went down. There was a discussion of this  
>> recently but nothing beats a step by step explanation.
>> 
>> 	Thanks, Joel
>> 
>> 
>> --
>> http://wagerlabs.com
>> 
>> 
>> 
>> 
>> 
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>> 
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