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responses/9034-response-2018-10-15.md

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+# Don’t Settle for Eventual: Scalable Causal Consistency for Wide-Area Storage with COPS
+
+Wyatt Lloyd, Michael J. Freedman, Michael Kaminsky, and David G. Andersen
+
+## Summary
+
+The authors introduce Causal+ consistency, or causal consistency with 
+convergent conflict resolution. For the conflic resolution, they use the
+principle of "last writer wins". They present COPS, a rather lazily 
+acronymed Key-Value store built on this idea, and support transactions in 
+COPS-GT an even more lazily named modification of the key value store.
+
+The authors state that the earlier implementations were Causal+ too, but did
+not have great scalability. The system they have in mind is an ALPS system
+Availability, Low Latency, Partition-tolerance and Scalability being the
+important required properties.
+
+Since linearizability is impossible to achieve in this scenario, the best
+level of consistency you can guarantee is Causal. However Causality places
+no restrictions on partitions diverging permanently with different data. 
+This is however a desirable property, and that's where the convergent 
+conflict resolution is required.
+
+The conflict detection adds a dependency on the previous version for key 
+update, causing a dependency check to happen, in order to detect conflicts
+which then are resolved using the last write wins rule.
+
+## Interesting Points
+
+The chief contribution of this paper is the scalable convergent conflict 
+handling the COPS system offers. However the paper seems to be split upon
+what to talk about. It talks about ALPS, and a significant chunk of the 
+paper is dedicated to the key value store and its evaluation, but from my
+understanding of it, COPS is a proof of concept rather than a key-value
+store they plan to release or design. 
+
+It just seemed to me that more space could have been given the the conflict
+handline (relegated to 1 paragraph) as opposed to the client libraries and 
+consistency models.
+
+The results look good, however the comparison with other systems seems to 
+bee limited and focused on only LOG exchange. The dependency vs throughput
+graphs are useful, but most of the evaluation is limited to COPS and COPS-GT
+
+
+## Research level question
+
+The authors claim that Causal+ consistency (done their way) is the best 
+possible consistency condition you can get for a system that focuses on 
+ALPS. Is this true? Can you do better?
+
+## Closing thoughts
+
+I do not think the paper was well written. It is extremely self indulgent
+(we are the first/ this is the best possible multiple times) and makes some
+bold claims for what seems to be a fairly straightforward idea. 
+
+The paper isn't well organized or written, it is repetitive, it focuses on
+minute details where unnecessary and glosses over where it would have been
+helpful, it is repetitive.