111,317 research outputs found
Causal Consistency: Beyond Memory
In distributed systems where strong consistency is costly when not
impossible, causal consistency provides a valuable abstraction to represent
program executions as partial orders. In addition to the sequential program
order of each computing entity, causal order also contains the semantic links
between the events that affect the shared objects -- messages emission and
reception in a communication channel , reads and writes on a shared register.
Usual approaches based on semantic links are very difficult to adapt to other
data types such as queues or counters because they require a specific analysis
of causal dependencies for each data type. This paper presents a new approach
to define causal consistency for any abstract data type based on sequential
specifications. It explores, formalizes and studies the differences between
three variations of causal consistency and highlights them in the light of
PRAM, eventual consistency and sequential consistency: weak causal consistency,
that captures the notion of causality preservation when focusing on convergence
; causal convergence that mixes weak causal consistency and convergence; and
causal consistency, that coincides with causal memory when applied to shared
memory.Comment: 21st ACM SIGPLAN Symposium on Principles and Practice of Parallel
Programming, Mar 2016, Barcelone, Spai
On the S-matrix renormalization in effective theories
This is the 5-th paper in the series devoted to explicit formulating of the
rules needed to manage an effective field theory of strong interactions in
S-matrix sector. We discuss the principles of constructing the meaningful
perturbation series and formulate two basic ones: uniformity and summability.
Relying on these principles one obtains the bootstrap conditions which restrict
the allowed values of the physical (observable) parameters appearing in the
extended perturbation scheme built for a given localizable effective theory.
The renormalization prescriptions needed to fix the finite parts of
counterterms in such a scheme can be divided into two subsets: minimal --
needed to fix the S-matrix, and non-minimal -- for eventual calculation of
Green functions; in this paper we consider only the minimal one. In particular,
it is shown that in theories with the amplitudes which asymptotic behavior is
governed by known Regge intercepts, the system of independent renormalization
conditions only contains those fixing the counterterm vertices with
lines, while other prescriptions are determined by self-consistency
requirements. Moreover, the prescriptions for cannot be taken
arbitrary: an infinite number of bootstrap conditions should be respected. The
concept of localizability, introduced and explained in this article, is closely
connected with the notion of resonance in the framework of perturbative QFT. We
discuss this point and, finally, compare the corner stones of our approach with
the philosophy known as ``analytic S-matrix''.Comment: 28 pages, 10 Postscript figures, REVTeX4, submitted to Phys. Rev.
Data consistency: toward a terminological clarification
The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-319-21413-9_15Consistency is an inconsistency are ubiquitous term in
data engineering. Its relevance to quality is obvious, since consistency
is a commonplace dimension of data quality. However, connotations are
vague or ambiguous. In this paper, we address semantic consistency,
transaction consistency, replication consistency, eventual consistency and
the new notion of partial consistency in databases. We characterize their
distinguishing properties, and also address their differences, interactions
and interdependencies. Partial consistency is an entry door to living with
inconsistency, which is an ineludible necessity in the age of big data.Decker and F.D. Muñoz—supported by the Spanish MINECO grant TIN 2012-37719-C03-01.Decker, H.; Muñoz EscoĂ, FD.; Misra, S. (2015). Data consistency: toward a terminological clarification. En Computational Science and Its Applications -- ICCSA 2015: 15th International Conference, Banff, AB, Canada, June 22-25, 2015, Proceedings, Part V. Springer International Publishing. 206-220. https://doi.org/10.1007/978-3-319-21413-9_15S206220Abadi, D.: Consistency tradeoffs in modern distributed database system design: Cap is only part of the story. Computer 45(2), 37–42 (2012)Bailis, P. (2015). http://www.bailis.org/blog/Bailis, P., Ghodsi, A.: Eventual consistency today: limitations, extensions, and beyond. ACM Queue, 11(3) (2013)Balegas, V., Duarte, S., Ferreira, C., Rodrigues, R., Preguica, N., Najafzadeh, M., Shapiro, M.: Putting consistency back into eventual consistency. In: 10th EuroSys. 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Idea Group (2002)Decker, H.: Historical and computational aspects of paraconsistency in view of the logic foundation of databases. In: Bertossi, L., Katona, G.O.H., Schewe, K.-D., Thalheim, B. (eds.) Semantics in Databases 2001. LNCS, vol. 2582, pp. 63–81. Springer, Heidelberg (2003)Decker, H.: Answers that have integrity. In: Schewe, K.-D., Thalheim, B. (eds.) SDKB 2010. LNCS, vol. 6834, pp. 54–72. Springer, Heidelberg (2011)Decker, H.: New measures for maintaining the quality of databases. In: Murgante, B., Gervasi, O., Misra, S., Nedjah, N., Rocha, A.M.A.C., Taniar, D., Apduhan, B.O. (eds.) ICCSA 2012, Part IV. LNCS, vol. 7336, pp. 170–185. Springer, Heidelberg (2012)Decker, H.: A pragmatic approach to model, measure and maintain the quality of information in databases (2012). www.iti.upv.es/~hendrik/papers/ahrc-workshop_quality-of-data.pdf , www.iti.upv.es/~hendrik/papers/ahrc-workshop_quality-of-data_comments.pdf . Slides and comments presented at the Workshop on Information Quality. Univ, Hertfordshire, UKDecker, H.: Answers that have quality. In: Murgante, B., Misra, S., Carlini, M., Torre, C.M., Nguyen, H.-Q., Taniar, D., Apduhan, B.O., Gervasi, O. (eds.) ICCSA 2013, Part II. LNCS, vol. 7972, pp. 543–558. Springer, Heidelberg (2013)Decker, H.: Measure-based inconsistency-tolerant maintenance of database integrity. In: Schewe, K.-D., Thalheim, B. (eds.) SDKB 2013. LNCS, vol. 7693, pp. 149–173. Springer, Heidelberg (2013)Decker, H., Martinenghi, D.: Inconsistency-tolerant integrity checking. IEEE Transactions of Knowledge and Data Engineering 23(2), 218–234 (2011)Decker, H., Muñoz-EscoĂ, F.D.: Revisiting and improving a result on integrity preservation by concurrent transactions. In: Meersman, R., Dillon, T., Herrero, P. (eds.) OTM 2010. LNCS, vol. 6428, pp. 297–306. 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The Weakest Failure Detector for Eventual Consistency
In its classical form, a consistent replicated service requires all replicas
to witness the same evolution of the service state. Assuming a message-passing
environment with a majority of correct processes, the necessary and sufficient
information about failures for implementing a general state machine replication
scheme ensuring consistency is captured by the {\Omega} failure detector. This
paper shows that in such a message-passing environment, {\Omega} is also the
weakest failure detector to implement an eventually consistent replicated
service, where replicas are expected to agree on the evolution of the service
state only after some (a priori unknown) time. In fact, we show that {\Omega}
is the weakest to implement eventual consistency in any message-passing
environment, i.e., under any assumption on when and where failures might occur.
Ensuring (strong) consistency in any environment requires, in addition to
{\Omega}, the quorum failure detector {\Sigma}. Our paper thus captures, for
the first time, an exact computational difference be- tween building a
replicated state machine that ensures consistency and one that only ensures
eventual consistency
Scalable Persistent Storage for Erlang
The many core revolution makes scalability a key property. The RELEASE project aims to improve the scalability of Erlang on emergent commodity architectures with 100,000 cores. Such architectures require scalable and available persistent storage on up to 100 hosts. We enumerate the requirements for scalable and available persistent storage, and evaluate four popular Erlang DBMSs against these requirements. This analysis shows that Mnesia and CouchDB are not suitable persistent storage at our target scale, but Dynamo-like NoSQL DataBase Management Systems (DBMSs) such as Cassandra and Riak potentially are. We investigate the current scalability limits of the Riak 1.1.1 NoSQL DBMS in practice on a 100-node cluster. We establish for the first time scientifically the scalability limit of Riak as 60 nodes on the Kalkyl cluster, thereby confirming developer folklore. We show that resources like memory, disk, and network do not limit the scalability of Riak. By instrumenting Erlang/OTP and Riak libraries we identify a specific Riak functionality that limits scalability. We outline how later releases of Riak are refactored to eliminate the scalability bottlenecks. We conclude that Dynamo-style NoSQL DBMSs provide scalable and available persistent storage for Erlang in general, and for our RELEASE target architecture in particular
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