采用内存数据访问对象提高数据库访问速度

将内存数据库的思想溶于传统磁盘数据库（DRDB）中，采用内存数据访问对象（MMDAO）技术，在当前主流计算机所能提供的有限内存中实现应用程序与数据库系统之间的接口，使数据库检索、存取等过程在内存中进行，避免大量的磁盘数据I／O，从而实现数据库应用程序中数据的高速存取、检索和操纵，提高应用系统的执行效率。     

嵌入式内存数据库在配料系统中的实现与应用

针对嵌入式配料系统采用单独的后台SQL数据库储存管理数据中存在的缺陷,提出了在嵌入式配料系统中采用前台内存数据库和后台SQL数据库协作的方式管理数据的全新解决方案.以某企业嵌入式配料系统项目为背景,研究了前台内存数据库和后台SQL数据库协作管理配料系统数据的实现过程,介绍了嵌入式内存数据库核心对象的数据组织方式.该方案已应用于嵌入式配料系统中,并使配料系统的实时性、可靠性、稳定性方面都得到了较大的提高.     

批处理在内存数据处理系统中的应用

内存数据处理相较磁盘数据处理有明显的速度优势.在基于磁盘的数据管理系统中,设计者往往会花很多精力对事务响应时间进行调优,以提高应用的用户体验.在内存数据管理系统中,由于存储介质的改变,事务响应时间得到极大提升,甚至远远超出应用系统的需求.因此,系统设计者将注意力转移到对吞吐率的优化上.批处理技术的本质是通过牺牲响应时间换取吞吐率,它将在内存计算中得到广泛应用.本文讨论批处理方式在内存数据管理系统中的应用,并以移动对象管理为实际案例,验证批处理在内存数据管理中的优化效果.     

内存数据库的可用性综述

随着计算机硬件技术的高速发展,内存的成本不断降低,数据库管理系统将其工作数据集完全放入内存变得可行.相比于常规的磁盘数据库,内存数据库具有更快的数据存储速度、更高的吞吐量和更强的并发访问能力,满足了许多应用的快速响应需求.然而,由于内存是易失性存储介质,与磁盘数据库在可用性方面有一定区别.本综述重点讨论了适用于内存数据库提高可用性的主要策略,包括快速恢复策略、冗余备份和容错等.     

基于WEB信息系统的优化管理及架构调整

论述了在Windows2000 Server平台上Oracle数据库的系统优化及其实现。在数据库服务器优化中,主要涉及了对内存和磁盘输入/输出的优化,内存的优化主要通过调整系统全局区(SGA)以提高内存的共享来实现;在应用程序结构设计中,实现了由单一的C/S模式向C/S、B/S混合模式的转变。     

ORACLE数据库服务器性能优化技术

ORACLE数据库的优化是通过合理分配计算机的资源(如内存、CPU、磁盘等)、调整系统运行参数来改进性能的过程,包括调整CPU参数、服务器内存分配、硬盘I/O、操作系统参数等几个部分.CPU使用率出现异常时要迅速找出原因,及时调整系统参数或优化SQL语句;内存参数的调整包括库缓冲区、数据字典缓冲区和缓冲区高速缓存的调整;影响磁盘I/O性能的主要原因有磁盘竞争、I/O次数过多和数据块空间的分配管理,使所有可用的磁盘均匀地平衡I/O,可以减少磁盘存取的时间;操作系统的调整要尽可能使ORA-CLE服务器使用资源最大化.在某单位"三流合一"项目中应用这些原则使服务器性能满足了系统的性能要求.     

大数据环境下Lucene性能优化方法研究

为提高大数据环境下的数据查询分析效率,该文结合内存计算技术和批量更新技术提出一种优化倒排索引方法——内存磁盘索引(RFDirectory)。基于Lucene实现内存和磁盘相结合的倒排表管理技术。将新增数据写入缓存中,并周期性地写入磁盘索引结构中,从而提升倒排索引的写入性能。通过整合磁盘和内存的多分块倒排结构,为用户提供高效的数据查询分析结果。实验结果表明:在大数据环境下,RFDirectory方法的索引构建时间缩短为磁盘索引(FSDirectory)、内存索引(RAMDirectory)方法索引构建时间的50%,返回1个关键字的检索结果耗时缩短了近15%。     

数据库集群服务器系统性能瓶颈分析

数据库集群服务器产品是采用集群作为基础的体系架构,它不单单是一个硬件平台,还包括了操作系统和数据库软件等。数据库软件就是提供了一种对数据进行操作的平台,因而数据在磁盘、内存、处理器之间移动过程中所产生的瓶颈也是最终系统体现出来的瓶颈。本文将主要从内存访问、进程间通信、磁盘IO访问等因素进行分析,从中可以看出系统性能提升的瓶颈及解决办法。     

论软件体系结构中的持久化技术

持久化,即"Persistence"。所谓将数据持久化就是将数据从内存中保存到磁盘中,也就是我们通常所说的将Java代码中的数据写入到数据库中,这样的话,哪怕系统掉电也能重新恢复数据。虽然持久化数据的方式多种多样,比如我们可以将数据以文件、XML文件的形式保存到磁盘中,但通常是将数据保存到数据库中,这样可以快速的对数据进行增、删、改、查等操作。     

基于 P2P的VOD系统中数据缓存策略研究

提出了一种结合内存缓存与磁盘缓存的新型缓存策略.该策略在原有内存缓存基础上增加了磁盘缓存,数据从内存中被淘汰时,从磁盘缓存空间中选择合适磁盘分片进行缓存,并建立索引管理已缓存数据,使对等网络中的节点利用彼此的闲置磁盘资源缓存更多的媒体数据,服务器的负载得到有效降低,节点在对等网络中从其他节点获取数据的成功率明显提高.实验证明,该缓存策略有效提高了系统的整体服务能力,充分利用对等网络中的空闲节点资源降低视频服务器的负载.     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

A computer generator for randomly layered structures

AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the