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From Michael Dürig <mdue...@apache.org>
Subject Re: [jr3 microkernel] Write skew
Date Thu, 01 Dec 2011 13:47:59 GMT

>> Currently the microkernel does nothing about this. That's what this whole
>> discussion is about after all ;-)
>
> and please bear in mind that the microkernel project in the jackrabbit sandbox
> is a prototype and represents WIP... ;)

I do. That's exactly why we should challenge it: to discover possible 
paint points and to discuss how to handle them.

Michael

>
> cheers
> stefan
>
>
>>
>> Eventually consistent approaches are IMO very hard to get right with JCR
>> since most operation are assumed to be persisted after dispatch. One
>> solution I see is to have changes caused by conflict resolution (i.e. during
>> convergence) to appear as normal changes as if they where done by other
>> sessions (see [1]). This would however require changing the revision model
>> of the microkernel from linear shaped to tree shaped.
>>
>> For the current problem I'd rather have the microkernel to expose some
>> test-and-set semantics as Tom describes in [2]. That way a client of the
>> microkernel could apply changes atomically.
>>
>> A third and most general solution which puts away with write skew for good
>> is described in [3]. This requires examining the commit log for certain
>> read-write conflicts on save.
>>
>> Michael
>>
>> [1]
>> http://wiki.apache.org/jackrabbit/Clustering%20the%20Microkernel#Replication
>>
>> [2] http://markmail.org/message/c32jpeoxklgcrybr
>>
>> [3] http://dl.acm.org/citation.cfm?id=1376690

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