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From Michael Dürig <mdue...@apache.org>
Subject Re: oak's consistency tuning options
Date Tue, 04 Sep 2012 11:02:27 GMT

Hi Tyson,

The current direction we are going is that clients may not make too much 
assumptions on consistency. That is, we effectively trade consistency 
for availability [1, 2].

In recent discussions about locking [3] and referential integrity [4] 
this issue surfaced again. There I suggested to provide lock support for 
non clustered setups and provide a hook where lock support could be 
plugged in for other cases. This way custom lock implementation - 
possibly through external coordinators like Apache Zookeeper - are still 
possible [5].

I think this approach could be further generalised such that consistency 
guarantees in general would be enforced through an pluggable/external 


[2] http://markmail.org/thread/kypn7c4bi5gjnspu
[3] https://issues.apache.org/jira/browse/OAK-150
[4] https://issues.apache.org/jira/browse/OAK-270

On 1.9.12 0:08, Tyson Norris wrote:
> Hi  -
> I was wondering if there are plans to surface consistency options in oak such that certain
save() operations can be guaranteed to be replicated?
> For example, in mongo getLastError() [0] can be executed with parameters to indicate
that the call will block until a certain level of consistency is achieved (write has reached
the server, write has been replicated to n nodes, write has been written to journal, etc)
> Are there any examples of how oak might provide this type of function, so that applications
could implement features where certain write operations block until consistency is achieved,
and other write operations never block?
> Thanks
> Tyson
> [0]http://www.mongodb.org/display/DOCS/getLastError+Command

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