Showing papers by "Francesco Quaglia published in 2011"

OSARE: Opportunistic Speculation in Actively REplicated Transactional Systems

Abstract: In this work we present OSARE, an active replication protocol for transactional systems that combines the usage of Optimistic Atomic Broadcast with a speculative concurrency control mechanism in order to overlap transaction processing and replica synchronization. OSARE biases the speculative serialization of transactions towards an order aligned with the optimistic message delivery order. However, due to the lock-free nature of its concurrency control algorithm, at high concurrency levels, namely when the probability of mismatches between optimistic and final deliveries is higher, OSARE explores additional alternative transaction serialization orders in a lightweight and opportunistic fashion. A simulation study we carried out in the context of Software Transactional Memory systems shows that OSARE achieves robust performance also in scenarios characterized by non-minimal likelihood of reorder between optimistic and final deliveries, providing remarkable speed-up with respect to state of the art speculative replication protocols.

The ROme OpTimistic Simulator: core internals and programming model

Abstract: In this article we overview the ROme OpTimistic Simulator (ROOT-Sim), an open source C/MPI-based simulation package targeted at POSIX systems, which implements a general-purpose parallel/distributed simulation environment relying on the optimistic (i.e., rollback based) synchronization paradigm. It offers a very simple programming model based on the classical notion of simulation-event handlers, to be implemented according to the ANSI-C standard, and transparently supports all the services required to parallelize the execution. It also offers a set of optimized protocols (e.g. CPU scheduling and state log/restore protocols) aimed at minimizing the run-time overhead of the platform, thus allowing for high performance and scalability. Here we overview the core internal mechanisms provided by ROOT-Sim, together with the offered APIs and the programming model that is expected to be agreed in order to produce simulation software that can be transparently run, in a concurrent fashion, on top of the ROOT-Sim layer.

Application Transparent Migration of Simulation Objects with Generic Memory Layout

Abstract: This paper presents the design of a global memory management architecture supporting application transparent migration of simulation objects (or LPs) whose state is scattered across dynamically allocated memory chunks. Our approach is based on a non-intrusive background protocol that provides each instance of the simulation kernel with information on the current mapping of the virtual address space of all the other instances. Dynamic memory requests by the application layer are then locally mapped onto virtual-address ranges that maximize the likelihood of being portable onto the address space of a remote kernel instance. In this way, independently of the load-balancing trigger (or policy), we maximize the likelihood that a desirable migration across a specific couple of kernels can actually take place due to compliance of the corresponding source/destination address spaces. We have integrated the global memory manager within the ROme OpTimistic Simulator (ROOT-Sim), namely a run-time environment based on the optimistic synchronization paradigm which automatically and transparently parallelizes the execution of event-handler based simulation programs conforming to ANSI-C. Further, we provide a contribution in the direction of widening load balancing schemes for optimistic simulation systems by defining migration triggers and selection policies for the objects to be migrated on the basis of memory usage patterns. An experimental assessment of the architecture and of memory oriented load balancing is also provided.

Integrated monitoring of infrastructures and applications in cloud environments

Abstract: One approach to fully exploit the potential of Cloud technologies consists in leveraging on the Autonomic Computing paradigm. It could be exploited in order to put in place reconfiguration strategies spanning the whole protocol stack, starting from the infrastructure and then going up to platform/application level protocols. On the other hand, the very base for the design and development of Cloud oriented Autonomic Managers is represented by monitoring sub-systems, able to provide audit data related to any layer within the stack. In this article we present the approach that has been taken while designing and implementing the monitoring sub-system for the Cloud-TM FP7 project, which is aimed at realizing a self-adapting, Cloud based middleware platform providing transactional data access to generic customer applications.

An evolutionary algorithm to optimize log/restore operations within optimistic simulation platforms

Abstract: In this work we address state recoverability in advanced optimistic simulation systems by proposing an evolutionary algorithm to optimize at run-time the parameters associated with state log/restore activities. Optimization takes place by adaptively selecting for each simulation object both (i) the best suited log mode (incremental vs non-incremental) and (ii) the corresponding optimal value of the log interval. Our performance optimization approach allows to indirectly cope with hidden effects (e.g., locality) as well as cross-object effects due to the variation of log/restore parameters for different simulation objects (e.g., rollback thrashing). Both of them are not captured by literature solutions based on analytical models of the overhead associated with log/restore tasks. More in detail, our evolutionary algorithm dynamically adjusts the log/restore parameters of distinct simulation objects as a whole, towards a well suited configuration. In such a way, we prevent negative effects on performance due to the biasing of the optimization towards individual simulation objects, which may cause reduced gains (or even decrease) in performance just due to the aforementioned hidden and/or cross-object phenomena. We also present an application-transparent implementation of the evolutionary algorithm within the ROme OpTimistic Simulator (ROOT-Sim), namely an open source, general purpose simulation environment designed according to the optimistic synchronization paradigm. Further, we provide the results of an experimental study testing our proposal on a suite of simulation models for wireless communication systems.

Providing e-Transaction Guarantees in Asynchronous Systems with No Assumptions on the Accuracy of Failure Detection

Abstract: In this paper, we address reliability issues in three-tier systems with stateless application servers. For these systems, a framework called e-Transaction has been recently proposed, which specifies a set of desirable end-to-end reliability guarantees. In this article, we propose an innovative distributed protocol providing e-Transaction guarantees in the general case of multiple, autonomous back-end databases (typical of scenarios with multiple parties involved within a same business process). Differently from existing proposals coping with the e-Transaction framework, our protocol does not rely on any assumption on the accuracy of failure detection. Hence, it reveals suited for a wider class of distributed systems. To achieve such a target, our protocol exploits an innovative scheme for distributed transaction management (based on ad hoc demarcation and concurrency control mechanisms), which we introduce in this paper. Beyond providing the proof of protocol correctness, we also discuss hints on the protocol integration with conventional systems (e.g., database systems) and show the minimal overhead imposed by the protocol.