76 research outputs found
An optimized conflict-free replicated set
Eventual consistency of replicated data supports concurrent updates, reduces
latency and improves fault tolerance, but forgoes strong consistency.
Accordingly, several cloud computing platforms implement eventually-consistent
data types. The set is a widespread and useful abstraction, and many replicated
set designs have been proposed. We present a reasoning abstraction, permutation
equivalence, that systematizes the characterization of the expected concurrency
semantics of concurrent types. Under this framework we present one of the
existing conflict-free replicated data types, Observed-Remove Set. Furthermore,
in order to decrease the size of meta-data, we propose a new optimization to
avoid tombstones. This approach that can be transposed to other data types,
such as maps, graphs or sequences.Comment: No. RR-8083 (2012
Concurrence control for transactions with priorities
Priority inversion occurs when a process is delayed by the actions of another process with less priority. With atomic transactions, the concurrency control mechanism can cause delays, and without taking priorities into account can be a source of priority inversion. Three traditional concurrency control algorithms are extended so that they are free from unbounded priority inversion
Dynamic Monopolies in Colored Tori
The {\em information diffusion} has been modeled as the spread of an
information within a group through a process of social influence, where the
diffusion is driven by the so called {\em influential network}. Such a process,
which has been intensively studied under the name of {\em viral marketing}, has
the goal to select an initial good set of individuals that will promote a new
idea (or message) by spreading the "rumor" within the entire social network
through the word-of-mouth. Several studies used the {\em linear threshold
model} where the group is represented by a graph, nodes have two possible
states (active, non-active), and the threshold triggering the adoption
(activation) of a new idea to a node is given by the number of the active
neighbors.
The problem of detecting in a graph the presence of the minimal number of
nodes that will be able to activate the entire network is called {\em target
set selection} (TSS). In this paper we extend TSS by allowing nodes to have
more than two colors. The multicolored version of the TSS can be described as
follows: let be a torus where every node is assigned a color from a finite
set of colors. At each local time step, each node can recolor itself, depending
on the local configurations, with the color held by the majority of its
neighbors. We study the initial distributions of colors leading the system to a
monochromatic configuration of color , focusing on the minimum number of
initial -colored nodes. We conclude the paper by providing the time
complexity to achieve the monochromatic configuration
Concurrency control for transactions with priorities
Priority inversion occurs when a process is delayed by the actions of another process with less priority. With atomic transations, the concurrency control mechanism can cause delays, and without taking priorities into account can be a source of priority inversion. In this paper, three traditional concurrency control algorithms are extended so that they are free from unbounded priority inversion
Multicolored Dynamos on Toroidal Meshes
Detecting on a graph the presence of the minimum number of nodes (target set)
that will be able to "activate" a prescribed number of vertices in the graph is
called the target set selection problem (TSS) proposed by Kempe, Kleinberg, and
Tardos. In TSS's settings, nodes have two possible states (active or
non-active) and the threshold triggering the activation of a node is given by
the number of its active neighbors. Dealing with fault tolerance in a majority
based system the two possible states are used to denote faulty or non-faulty
nodes, and the threshold is given by the state of the majority of neighbors.
Here, the major effort was in determining the distribution of initial faults
leading the entire system to a faulty behavior. Such an activation pattern,
also known as dynamic monopoly (or shortly dynamo), was introduced by Peleg in
1996. In this paper we extend the TSS problem's settings by representing nodes'
states with a "multicolored" set. The extended version of the problem can be
described as follows: let G be a simple connected graph where every node is
assigned a color from a finite ordered set C = {1, . . ., k} of colors. At each
local time step, each node can recolor itself, depending on the local
configurations, with the color held by the majority of its neighbors. Given G,
we study the initial distributions of colors leading the system to a k
monochromatic configuration in toroidal meshes, focusing on the minimum number
of initial k-colored nodes. We find upper and lower bounds to the size of a
dynamo, and then special classes of dynamos, outlined by means of a new
approach based on recoloring patterns, are characterized
The design of Wren, a Fast and Scalable Transactional Causally Consistent Geo-Replicated Key-Value Store
This paper presents the design of Wren, a new geo-replicated key-value store that achieves Transactional Causal Consistency. Wren leverages two design choices to achieve higher performance and better scalability than existing systems. First, Wren uses hybrid logical physical/clocks to timestamp data items. Hybrid clocks allow Wren to achieve low response times, by avoiding the latencies that existing systems based on physical clocks incur to cope with clock skew. Second, Wren relies on a novel dependency tracking and stabilization protocol, called Hybrid Stable Time (HST). HST uses only two scalar values per update regardless of the number of data centers and nodes within a data center. HST achieves high resource efficiency and scalability at the cost of a slight increase in remote update visibility latency. We discuss why Wren achieves higher performance and better scalability than state-of-the-art approaches
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