GentleRain: Cheap and Scalable Causal Consistency with Physical Clocks

GentleRain is a new causally consistent geo-replicated data store that provides throughput comparable to eventual consistency and superior to current implementations of causal consistency. GentleRain uses a periodic aggregation protocol to deter- mine whether updates can be made visible in accordance with causal consistency. Unlike current implementations, it does not use explicit dependency check messages, result- ing in a major throughput improvement at the expense of a modest increase in update visibility. Furthermore, GentleRain tracks causal consistency by attaching to updates scalar timestamps derived from loosely synchronized physical clocks. Clock skew does not cause violations of causal consistency, but may delay the visibility of updates. By en- coding causality in a single scalar timestamp, GentleRain reduces storage and communication overhead for tracking causality. We evaluate GentleRain using Amazon EC2, and demonstrate that it achieves throughput equal to about 99% of eventual consistency, and 120% better than previous implementations of causal consistency

The Loss of Telomerase Activity in Highly Differentiated CD8+CD28−CD27− T Cells Is Associated with Decreased Akt (Ser473) Phosphorylation

The enzyme telomerase is essential for maintaining the replicative capacity of memory T cells. Although CD28 costimulatory signals can up-regulate telomerase activity, human CD8 + T cells lose CD28 expression after repeated activation. Nevertheless, telomerase is still inducible in CD8 + CD28 − T cells. To identify alternative costimulatory pathways that may be involved, we introduced chimeric receptors containing the signaling domains of CD28, CD27, CD137, CD134, and ICOS in series with the CD3 zeta (ζ) chain into primary human CD8 + T cells. Although CD3 ζ-chain signals alone were ineffective, triggering of all the other constructs induced proliferation and telomerase activity. However, not all CD8 + CD28 − T cells could up-regulate this enzyme. The further fractionation of CD8 + CD28 − T cells into CD8 + CD28 − CD27 + and CD8 + CD28 − CD27 − subsets showed that the latter had significantly shorter telomeres and extremely poor telomerase activity. The restoration of CD28 signaling in CD8 + CD28 − CD27 − T cells could not reverse the low telomerase activity that was not due to decreased expression of human telomerase reverse transcriptase, the enzyme catalytic subunit. Instead, the defect was associated with decreased phosphorylation of the kinase Akt, that phosphorylates human telomerase reverse transcriptase to induce telomerase activity. Furthermore, the defective Akt phosphorylation in these cells was specific for the Ser 473 but not the Thr 308 phosphorylation site of this molecule. Telomerase down-regulation in highly differentiated CD8 + CD28 − CD27 − T cells marks their inexorable progress toward a replicative end stage after activation. This limits the ability of memory CD8 + T cells to be maintained by continuous proliferation in vivo

Write Fast, Read in the Past: Causal Consistency for Client-side Applications

International audienceClient-side apps (e.g., mobile or in-browser) need cloud data to be available in a local cache, for both reads and updates. For optimal user experience and developer support, the cache should be consistent and fault-tolerant. In order to scale to high numbers of unreliable and resource-poor clients, and large database, the system needs to use resources sparingly. The SwiftCloud distributed object database is the first to provide fast reads and writes via a causally-consistent client-side local cache backed by the cloud. It is thrifty in resources and scales well, thanks to consistent versioning provided by the cloud, using small and bounded metadata. It remains available during faults, switching to a different data centre when the current one is not responsive, while maintaining its consistency guarantees. This paper presents the SwiftCloud algorithms, design, and experimental evaluation. It shows that client-side apps enjoy the high performance and availability, under the same guarantees as a remote cloud data store, at a small cost

Context-aware state management for ubiquitous applications

In a ubiquitous computing environment, users continuously access computing services and interact with smart spaces, while moving from one place to another. Application migration, therefore, is an important and necessary feature. State capturing, migration and restoration play a significant role to enable application migration. However, current software systems usually capture the state at the source and restore it in the destination as it is, without any modification. We believe that application migration in the ubiquitous computing environment has to be context-aware. In this paper, we introduce a context-aware state capturing and restoring mechanism that can achieve context-aware application migration. Our context-aware migration scheme has been implemented in our Sparkle Pervasive Environment, and we demonstrate it with a Universal Browser Application. We believe with this mechanism, applications can be more adaptive to the changing environment as the internal program states will be processed to suit the new context environment at the destination device and mobile code could be brought in from the network to adapt to the new execution context. © Springer-Verlag Berlin Heidelberg 2004.link_to_subscribed_fulltex

Integration of apoptosis and telomere erosion in virus-specific CD8+ T cells from blood and tonsils during primary infection.

Human-virus-specific CD8+ T cells that are found during primary infection have been studied almost exclusively in the peripheral blood, and it is unclear whether these cells are regulated in the same way as those in secondary lymphoid tissue. We investigated, therefore, the control of apoptosis and telomere erosion of Epstein-Barr virus (EBV)-specific CD8+ T cells found in the blood and tonsils of the same patients during acute infectious mononucleosis (AIM). Although the clonal composition of CD8+ T cells as determined by heteroduplex analysis was similar in both compartments, there was greater CD28 expression in the tonsil population, indicating that they were less differentiated. EBV-specific CD8+ T cells in both tissue types were extremely susceptible to apoptosis related to low Bcl-2 expression and were dependent on exogenous cytokines such as interleukin-2 (IL-2), IL-15, and interferon-alpha/beta (IFN-alpha/beta) for survival. In both compartments, however, these cells maintained their telomere lengths through telomerase induction. Thus, apoptosis-prone EBV-specific CD8+ T cells found during acute infection have to be rescued from death to persist as a memory population. However, signals that induce telomerase ensure that the rescued cells retain their replicative capacity. Significantly, these processes operate identically in cells found in blood and secondary lymphoid tissue