336 research outputs found
Efficient simulation of view synchrony
This report presents an algorithm for efficiently simulating view synchrony, including failure-atomic total-order multicast in a discrete-time event simulator. In this report we show how a view synchrony implementation tailored to a simulated environment removes the need for third party middleware and detailed network simulation, thus reducing the complexity of a test environment. An additional advantage is that simulated view synchrony can generate all timing behaviours allowed by the model instead of just those exhibited by a particular view synchrony implementation
Atomic commitment in transactional DHTs
We investigate the problem of atomic commit in transactional database systems
built on top of Distributed Hash Tables. DHTs provide a decentralized way to
store and look up data. To solve the atomic commit problem we propose to
use an adaption of Paxos commit as a non-blocking algorithm. We exploit the
symmetric replication technique existing in the DKS DHT to determine which
nodes are necessary to execute the commit algorithm. By doing so we achieve a
lower number of communication rounds and a reduction of meta-data in contrast
to traditional Three-Phase-Commit protocols. We also show how the proposed
solution can cope with dynamism due to churn in DHTs. Our solution works
correctly relying only on an inaccurate failure detection of node failure which is
necessary for systems running over the Internet
Kompics: a message-passing component model for building distributed systems
The Kompics component model and programming framework was designedto simplify the development of increasingly complex distributed systems. Systems built with Kompics leverage multi-core machines out of the box and they can be dynamically reconfigured to support hot software upgrades. A simulation framework enables deterministic debugging and reproducible performance evaluation of unmodified Kompics distributed systems.
We describe the component model and show how to program and compose event-based distributed systems. We present the architectural patterns and abstractions that Kompics facilitates and we highlight a case study of a complex
distributed middleware that we have built with Kompics. We show how our approach enables systematic development and evaluation of large-scale and dynamic distributed systems
Moving the shared memory closer to the processors: DDM
Multiprocessors with shared memory are considered more general and easier
to program than message-passing machines. The scalability is, however, in favor
of the latter. There are a number of proposals showing how the poor scalability
of shared memory multiprocessors can be improved by the introduction of private
caches attached to the processors. These caches are kept consistent with each
other by cache-coherence protocols.
In this paper we introduce a new class of architectures called Cache Only
Memory Architectures (COMA). These architectures provide the programming
paradigm of the shared-memory architectures, but are believed to be more scal-
able. COMAs have no physically shared memory; instead, the caches attached to
the processors contain all the memory in the system, and their size is therefore
large. A datum is allowed to be in any or many of the caches, and will automatically be moved to where it is needed by a cache-coherence protocol, which also
ensures that the last copy of a datum is never lost. The location of a datum in
the machine is completely decoupled from its address.
We also introduce one example of COMA: the Data Diffusion Machine (DDM).
The DDM is based on a hierarchical network structure, with processor/memory
pairs at its tips. Remote accesses generally cause only a limited amount of traffic
over a limited part of the machine.
The architecture is scalable in that there can be any number of levels in the
hierarchy, and that the root bus of the hierarchy can be implemented by several
buses, increasing the bandwidth
PENERAPAN PEMBELAJARAN GROUP INVESTIGATION UNTUK MENINGKATKAN HASIL BELAJAR MATEMATIKA SISWA KELAS X IPA 1 MAN 2 BANYUWANGI
Based on preliminary study, it is known that the students of class XIPA 1 MAN 2 Banyuwangi have problems in the learning process ofmathematics. Therefore, teachers need to seek solutions. Theteacher's efforts include applying cooperative learning model ofGroup investigation type. This study aims to determine: 1) Increasedmotivation and learning activities of mathematics throughcooperative learning model type of gruop investigation on studentsclass X IPA 1 MAN 2 Banyuwangi. 2) improving mathematicslearning outcomes through cooperative learning model type of gruopinvestigation on students class X IPA 1 MAN 2 Banyuwangi. Thisresearch is a classroom action research conducted on the subject ofMathematics. Subjects in the meticulous are students of Class X IPA1 MAN 2 Banyuwangi academic year 2017/2018. The researchprocedure consists of two cycles for 4 meetings. Each cycle iscarried out with activities: Planning, Action Implementation,Observation, Evaluation, Reflection. Analytical technique that willbe used is descriptive technique. The results showed: 1) there is anincrease in motivation and learning activities of mathematicsthrough cooperative learning model type of gruop investigation instudents of class X IPA 1 MAN 2 Banyuwangi. 2) there isimprovement of mathematics learning outcomes through cooperativelearning model type of gruop investigation in students of class XIPA 1 MAN 2 Banyuwangi
CATS: linearizability and partition tolerance in scalable and self-organizing key-value stores
Distributed key-value stores provide scalable, fault-tolerant, and self-organizing
storage services, but fall short of guaranteeing linearizable consistency
in partially synchronous, lossy, partitionable, and dynamic networks, when data
is distributed and replicated automatically by the principle of consistent hashing.
This paper introduces consistent quorums as a solution for achieving atomic
consistency. We present the design and implementation of CATS, a distributed
key-value store which uses consistent quorums to guarantee linearizability and partition tolerance in such adverse and dynamic network conditions. CATS is
scalable, elastic, and self-organizing; key properties for modern cloud storage
middleware. Our system shows that consistency can be achieved with practical
performance and modest throughput overhead (5%) for read-intensive workloads
Symmetric Replication for Structured Peer-to-Peer Systems
Structured peer-to-peer systems rely on replication as a basic means to provide fault-tolerance in presence of high churn. Most select replicas using either multiple hash functions, successor-lists, or leaf-sets. We show that all three alternatives have limitations. We present and provide full algorithmic speciÂŻcation for a generic replication scheme called symmetric replication which only needs O(1) message for every join and leave operation to maintain any replication degree. The scheme is applicable to all existing structured peer-to-peer systems, and can be implemented on-top of any DHT. The scheme has been implemented in our DKS system, and is used to do load-balancing, end-to-end fault-tolerance, and to increase the security by using distributed voting. We outline an extension to the scheme, implemented in DKS, which adds routing proximity to reduce latencies. The scheme is particularly suitable for use with erasure codes, as it can be used to fetch a random subset of
the replicas for decoding
Gozar: NAT-friendly Peer Sampling with One-Hop Distributed NAT Traversal
Gossip-based peer sampling protocols have been widely used as a building block for many large-scale distributed applications. However, Network Address Translation gateways (NATs) cause most existing gossiping protocols to break down, as nodes cannot establish direct connections to nodes behind NATs (private nodes). In addition, most of the existing NAT traversal algorithms for establishing connectivity to private nodes rely on third party servers running at a well-known, public IP addresses. In this paper, we present Gozar, a gossip-based peer sampling service that: (i) provides uniform random samples in the presence of NATs, and (ii) enables direct connectivity to sampled nodes using a fully distributed NAT traversal service, where connection messages require only a single
hop to connect to private nodes. We show in simulation that Gozar preserves the randomness properties of a gossip-based peer sampling service. We show the robustness of Gozar when a large fraction of nodes reside behind NATs and also in
catastrophic failure scenarios. For example, if 80% of nodes are behind NATs, and 80% of the nodes fail, more than 92% of the remaining nodes stay connected. In addition, we compare Gozar with existing NAT-friendly gossip-based peer sampling services, Nylon and ARRG. We show that Gozar is the only system that supports one-hop NAT traversal, and its overhead is roughly half of Nylon’s
NATCracker: NAT Combinations Matter
In this paper, we report our experience in working
with Network Address Translators (NATs). Traditionally, there
were only 4 types of NATs. For each type, the (im)possibility
of traversal is well-known. Recently, the NAT community has
provided a deeper dissection of NAT behaviors resulting into at
least 27 types and documented the (im)possibility of traversal
for some types. There are, however, two fundamental issues that
were not previously tackled by the community. First, given the
more elaborate set of behaviors, it is incorrect to reason about
traversing a single NAT, instead combinations must be considered
and we have not found any study that comprehensively states,
for every possible combination, whether direct connectivity with
no relay is feasible. Such a statement is the first outcome of the
paper. Second, there is a serious need for some kind of formalism
to reason about NATs which is a second outcome of this paper.
The results were obtained using our own scheme which is an
augmentation of currently-known traversal methods. The scheme
is validated by reasoning using our formalism, simulation and
implementation in a real P2P network
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