Cloudy Forecast: How Predictable is Communication Latency in the Cloud?

Many systems and services rely on timing assumptions for performance and availability to perform critical aspects of their operation, such as various timeouts for failure detectors or optimizations to concurrency control mechanisms. Many such assumptions rely on the ability of different components to communicate on time -- a delay in communication may trigger the failure detector or cause the system to enter a less-optimized execution mode. Unfortunately, these timing assumptions are often set with little regard to actual communication guarantees of the underlying infrastructure -- in particular, the variability of communication delays between processes in different nodes/servers. The higher communication variability holds especially true for systems deployed in the public cloud since the cloud is a utility shared by many users and organizations, making it prone to higher performance variance due to noisy neighbor syndrome. In this work, we present Cloud Latency Tester (CLT), a simple tool that can help measure the variability of communication delays between nodes to help engineers set proper values for their timing assumptions. We also provide our observational analysis of running CLT in three major cloud providers and share the lessons we learned

Stable successional patterns of aquatic hyphomycetes on leaves decaying in a summer cool stream.

The colonization of leaf litter (Alnus glutinosa) by aquatic hyphomycetes was studied in a summer cool stream of the French Pyrenees. In spite of the rapid decomposition of leaves, the fungal community exhibited a characteristic successional pattern with three phases. The initial colonization stage was defined by a dense sporulation of the five species Tetrachaetum elegans, Lemonniera aquatica, L. centrosphaera, L. terrestris, and in particular Flagellospora curvula. After four weeks of colonization, a mature community had established. It was characterized by high species diversity and peak fungal biomass, which was measured as ergosterol content, and coincided with about 50 % loss in leaf mass. With leaf decay progressing further, diversity diminished concomitant with a slight reduction in fungal biomass and a sharp decrease in the rate of conidial production. Typical species of this late successional stage were Clavatospora longibrachiata, Heliscella stellata and Goniopila monticola. This successional pattern proved to be stable both within the period of leaf fall in one year and between two successive years. Between-seasons differences were quite small as well, the striking lack of species replacement apparently being due to not exceeding the threshold temperature of 16-18 °C as previously defined in literature. In spite of this general stability in community structure, correspondence analysis discriminated the communities on leaf packs with equal exposure times according to season, with the cyclical arrangement of leaf packs on the principal factorial plane reflecting the seasonal cycle. The colonization of fresh (non-dried) leaf litter by aquatic hyphomycetes was delayed compared to air-dried litter; however, the lead diminished with progressing leaf decay, resulting in nearly identical communities on fresh and dried leaves after four weeks of decomposition

Fatty Acid Synthase Expression Is Induced by the Epstein-Barr Virus Immediate-Early Protein BRLF1 and Is Required for Lytic Viral Gene Expression

The Epstein-Barr virus (EBV) immediate-early (IE) protein BRLF1 (R) is a transcription factor that induces the lytic form of EBV infection. R activates certain early viral promoters through a direct binding mechanism but induces transcription of the other EBV IE gene, BZLF1 (Z), indirectly through cellular factors binding to a CRE motif in the Z promoter (Zp). Here we demonstrate that R activates expression of the fatty acid synthase (FAS) cellular gene through a p38 stress mitogen-activated protein kinase-dependent mechanism. B-cell receptor engagement of Akata cells also increases FAS expression. The FAS gene product is required for de novo synthesis of the palmitate fatty acid, and high-level FAS expression is normally limited to liver, brain, lung, and adipose tissue. We show that human epithelial tongue cells lytically infected with EBV (from oral hairy leukoplakia lesions) express much more FAS than uninfected cells. Two specific FAS inhibitors, cerulenin and C75, prevent R activation of IE (Z) and early (BMRF1) lytic EBV proteins in Jijoye cells. In addition, cerulenin and C75 dramatically attenuate IE and early lytic gene expression after B-cell receptor engagement in Akata cells and constitutive lytic viral gene expression in EBV-positive AGS cells. However, FAS inhibitors do not reduce lytic viral gene expression induced by a vector in which the Z gene product is driven by a strong heterologous promoter. In addition, FAS inhibitors do not reduce R activation of a naked DNA reporter gene construct driven by the Z promoter (Zp). These results suggest that cellular FAS activity is important for induction of Z transcription from the intact latent EBV genome, perhaps reflecting the involvement of lipid-derived signaling pathways or palmitoylated proteins. Furthermore, using FAS inhibitors may be a completely novel approach for blocking the lytic form of EBV replication