Fault Tolerance?

Mdecandia mdecandia at email.it
Fri Sep 28 07:50:24 UTC 2007

On Sep 27, 2007, at 22:16, Dustin Sallings write: 
> On Sep 27, 2007, at 21:56, Paul Scott wrote:
> >> Agreed. Wouldn’t it be great though to have a mem-based HA datastore?
> >
> > I would certainly vote +1 on that idea!
> 	You do realize you wouldn't have anything remotely like the  
> performance of memcached, don't you?  You'd need something along the  
> lines of two-phase-commit if you want any kind of correctness.  If  
> you don't want correctness, then why are you worried about HA?
We use memcached to store items fetched from a slow service, not from
Performance difference between this service and memcached are huge.
May be really convenient to have an HA feature on memcached servers.

> 	If you lose a node, how do you plan on rematerializing?  A complete  
> synchronization would block both nodes in a two-node cluster.

We've introduced libketama consistant hashing to reduce effects on server
faults but 
it will be useful to have a redundant caching system between servers to be
really fault toulerant.

> 	How would you handle conflicts during rematerialization after a  
> netsplit?
> 	Is it acceptable to block all clients during a netsplit (pending  
> some sort of magical synchronization that knows what to do when  
> conflicts occur)?
> 	After you get all of the pieces in place, are you sure you'd have  
> something that would be any faster than any solution that isn't  
> completely in-memory?
> -- 
> Dustin Sallings


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