[infinispan-issues] [JBoss JIRA] (ISPN-999) Support eventual consistency

[Dan Berindei (JIRA)]

    [ https://issues.jboss.org/browse/ISPN-999?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13003400#comment-13003400 ] 

Dan Berindei commented on ISPN-999:
-----------------------------------

I bumped the target version again, to 8.0, since we haven't made any progress on this yet.

> Support eventual consistency
> ----------------------------
>
>                 Key: ISPN-999
>                 URL: https://issues.jboss.org/browse/ISPN-999
>             Project: Infinispan
>          Issue Type: Feature Request
>          Components: Core, Transactions
>            Reporter: Manik Surtani
>            Assignee: Manik Surtani
>            Priority: Critical
>              Labels: eventual_consistency
>             Fix For: 8.0.0.Final
>
>   Original Estimate: 1 minute
>  Remaining Estimate: 1 minute
>
> Essentially, it is about supporting eventual consistency in Infinispan.  Currently Infinispan is strongly consistent when using synchronous distribution mode.  Each data owner receives updates synchronously so anyone anywhere on the cluster doing a GET will see the correct value.  The only exception is during a rehash (when a new node joins or leaves), that consistency is eventual since the GET may reach a new joiner who may not have applied state it receives from its neighbours yet.  However this is hidden from users since the GET is sent to>  1 data owner and if an UnsureResponse is received (determined by the fact that a new joiner responds and the new joiner wouldn't have finished applying state), the caller thread waits for more definite responses.
> However, there is a use case for being eventually consistent as well: the main benefits being speed and partition tolerance.  E.g., if we use distribution in asynchronous mode, the writes become *much* faster.  However, anyone anywhere doing a GET will have to perform the GET on all data owners, and compare the versions of the data received to determine which is the latest.  And if there is a conflict, to pass back all values to the user.
> So in terms of design, what I have in mind is:
> * All cache entries are versioned using vector clocks.  One vector clock per node.
> * When a node performs a GET, the GET is sent to all data owners (concurrently), and the value + version is retrieved from each.
> * If the versions are all the same (or they can be "fast forwarded"), the value is returned
> * Otherwise, all potential values and their versions are returned
> * A resolve() API should be provided where application code may provide a "hint" as to which version should be "correct" - which will cause an update.
> * In terms of implementation, this will touch the DistributionInterceptor, InternalCacheEntry and relevant factories, some config code (since this should be consistency model should be configurable), and a new public interface.



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