Online paging and file caching with expiration times

AbstractWe consider a paging problem in which each page is assigned an expiration time at the time it is brought into the cache. The expiration time indicates the latest time that the fetched copy of the page may be used. Requests that occur later than the expiration time must be satisfied by bringing a new copy of the page into the cache. The problem has applications in caching of documents on the World Wide Web (WWW). We show that a natural extension of the well-studied least recently used (LRU) paging algorithm is strongly competitive for the uniform retrieval cost, uniform size case. We then describe a similar extension of the recently proposed Landlord algorithm for the case of arbitrary retrieval costs and sizes, and prove that it is strongly competitive. The results extend to the loose model of competitiveness as well

Dissecting the Shared Genetic Architecture of Suicide Attempt, Psychiatric Disorders, and Known Risk Factors

Background Suicide is a leading cause of death worldwide, and nonfatal suicide attempts, which occur far more frequently, are a major source of disability and social and economic burden. Both have substantial genetic etiology, which is partially shared and partially distinct from that of related psychiatric disorders. Methods We conducted a genome-wide association study (GWAS) of 29,782 suicide attempt (SA) cases and 519,961 controls in the International Suicide Genetics Consortium (ISGC). The GWAS of SA was conditioned on psychiatric disorders using GWAS summary statistics via multitrait-based conditional and joint analysis, to remove genetic effects on SA mediated by psychiatric disorders. We investigated the shared and divergent genetic architectures of SA, psychiatric disorders, and other known risk factors. Results Two loci reached genome-wide significance for SA: the major histocompatibility complex and an intergenic locus on chromosome 7, the latter of which remained associated with SA after conditioning on psychiatric disorders and replicated in an independent cohort from the Million Veteran Program. This locus has been implicated in risk-taking behavior, smoking, and insomnia. SA showed strong genetic correlation with psychiatric disorders, particularly major depression, and also with smoking, pain, risk-taking behavior, sleep disturbances, lower educational attainment, reproductive traits, lower socioeconomic status, and poorer general health. After conditioning on psychiatric disorders, the genetic correlations between SA and psychiatric disorders decreased, whereas those with nonpsychiatric traits remained largely unchanged. Conclusions Our results identify a risk locus that contributes more strongly to SA than other phenotypes and suggest a shared underlying biology between SA and known risk factors that is not mediated by psychiatric disorders.Peer reviewe

The genetic architecture of the human cerebral cortex

The cerebral cortex underlies our complex cognitive capabilities, yet little is known about the specific genetic loci that influence human cortical structure. To identify genetic variants that affect cortical structure, we conducted a genome-wide association meta-analysis of brain magnetic resonance imaging data from 51,665 individuals. We analyzed the surface area and average thickness of the whole cortex and 34 regions with known functional specializations. We identified 199 significant loci and found significant enrichment for loci influencing total surface area within regulatory elements that are active during prenatal cortical development, supporting the radial unit hypothesis. Loci that affect regional surface area cluster near genes in Wnt signaling pathways, which influence progenitor expansion and areal identity. Variation in cortical structure is genetically correlated with cognitive function, Parkinson's disease, insomnia, depression, neuroticism, and attention deficit hyperactivity disorder

Interleaving Sequences to Maximize the Minimum Prefix Sum

We consider the problem of interleaving sequences of real numbers in order to maximize the minimum, over all prefixes p of the interleaved sequence, of the sum of the numbers in p. A simple and efficient solution is given. This problem is motivated by a resource scheduling application, and a special case of the scheduling problem is reduced to the interleaving problem

Parallel prefetching and caching

Thesis (Ph. D.)--University of Washington, 1997High-performance I/O systems depend on prefetching and caching to deliver good performance to applications. These two techniques have generally been considered in isolation, even though there are significant interactions between them: a block prefetched too early may cause a block that is needed soon to be evicted from the cache, thus reducing the effectiveness of the cache, while a block cached too long may reduce the effectiveness of prefetching by denying opportunities to the prefetcher. Using both analytical and experimental methods, we study the problem of integrated prefetching and caching for an I/O system with multiple disks.In a theoretical analysis, we consider algorithms for integrated prefetching and caching in a model abstracting relevant characteristics of file systems with multiple disks. Previously, the "aggressive" algorithm was shown by Cao, Felten, Karlin, and Li to have near-optimal performance in the single disk case. We show that the natural extension of the aggressive algorithm to the parallel disk case is suboptimal by a factor near the number of disks in the worst case. Our main theoretical result is a new algorithm, "reverse aggressive," with provably near-optimal performance in the presence of multiple disks.Using disk-accurate trace-driven simulation, we explore the performance characteristics of several algorithms in cases in which applications provide full advance knowledge of accesses using hints. The algorithms tested are the two mentioned previously, plus the "fixed horizon" algorithm of Patterson et al., and a new algorithm, "forestall," that combines the desirable characteristics of the others. We find that when performance is limited by I/O stalls, aggressive prefetching helps to alleviate the problem; that more conservative prefetching is appropriate when significant I/O stalls are not present; and that a single, simple strategy is capable of doing both.We also consider three related problems. First, we present an optimal algorithm for a restricted version of the single disk prefetching and caching problem. Next, we propose an approach to the integration of prefetching and caching policies with processor and disk scheduling policies. Finally, we show the NP-hardness of a problem of ordering requests to maximize locality of reference

Dynamic

application placement under service and memory constraint

Near-optimal Parallel Prefetching

Recently there has been a great deal of interest in prefetching from parallel disks, as a technique for enabling serial applications to improve I/O performance