[infinispan-dev] Eventual consistency

[Manik Surtani]

No, not all the time. To some degree, vector clock based versions can be merged, but as you say there are circumstances where manual intervention may be necessary. 

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On 2 Mar 2011, at 22:30, Bela Ban <bban at redhat.com> wrote:

> The thing is the a causal history does not lead to automatic merges all 
> the time; Dynamo for instance leaves it up to the app developer to 
> resolve merge conflicts by comparing vector clocks.
> 
> +1 for experimenting with an eventual consistency model in Infinispan
> 
> On 3/2/11 6:43 PM, Manik Surtani wrote:
>> As consistency models go, Infinispan is primarily strongly consistent (with 2-phase commit between data owners), with the exception of during a rehash where because of eventual consistency (inability to get a valid response to a remote GET) forces us to wait for more responses, a quorum if you like.  Not dissimilar to PAXOS [1] in some ways.
>> 
>> I'm wondering whether, for the sake of performance, we should also offer a fully eventually consistent model?  What I am thinking is that changes *always* occur only on the primary data owner.  Single phase, no additional round trips, etc.  The primary owner then asynchronously propagates changes to the other data owners.  This would mean things run much faster in a stable cluster, and durability is maintained.  However, during rehashes when keys are moved, the notion of the primary owner may change.  So to deal with this, we could use vector clocks [2] to version each entry.  Vector clocks allow us to "merge" state nicely in most cases, and in the case of reads, we'd flip back to a PAXOS style quorum during a rehash to get the most "correct" version.
>> 
>> In terms of implementation, almost all of this would only affect the DistributionInterceptor and the DistributionManager, so we could easily have eventually consistent flavours of these two components.
> 
> 
> -- 
> Bela Ban
> Lead JGroups / Clustering Team
> JBoss
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