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From Michael Dürig <mdue...@apache.org>
Subject Re: [jr3 microkernel] Write skew
Date Thu, 01 Dec 2011 21:36:12 GMT

On 1.12.11 14:25, Jukka Zitting wrote:
>> For the current problem I'd rather have the microkernel to expose some
>> test-and-set semantics as Tom describes in [2].
> A test-and-set operation necessarily requires at least some level of
> atomicity which can quickly become a bottleneck for a clustered setup.

Yes but that critical section can be very small: since the changes are 
written to disk ahead, locking is only required when writing the new 
revision id to the journal. With the test and set approach, the only 
addition is to do the test inside the lock. With (correct) double 
checked locking this can even be further optimized.


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