Oracle查询优化器之SQL转换初探

本文首先介绍Oracle的查询优化程序及其组成，它是数据库的关键组件之一，能让Oracle的用户获得极佳的执行性能。文章着重论述了在Oracle中优化程序对多种SQL语句的转换方式。接着给出了书写SQL的一些经验。根据这些知识可以帮助我们编写出更加高效、灵活的SQL语句，降低系统开销并减少系统开发过程中可能出现的低性能问题。     

Java调用Oracle存储过程的方法研究

存储过程是指保存在数据库并在数据库端执行的程序。存储过程在概念上类似于程序中的函数。它们获取输人参数，以黑盒模式运行并返回相应信息。与函数不同的是，存储过程由数据库引擎执行，而不是在程序中执行。也就是说，将信息输入到存储过程或从中输出信息都必须通过与数据库交互的技术来完成。使用存储过程，把SQL语句放到Oracle服务器端来执行，具有性能好、代码独立、并发性强、安全性高等优点。在Java程序中访问数据库，一般采用JDBC技术，JDBC是一项在Java中以面向对象的方法来连接数据库的技术，提供了多样化的数据库连接方式。     

基于Weblogic连接池获取SQL语句的实现

本文分析了Weblogic连接池的用法,给出了不修改程序直接获取系统所运行的SQL语句的方法,并列举出了关键的实例代码.     

基于面向对象程序的一种波动分析方法及其实现

“波动”一词从程序设计出现就已经产生。在程序中,各个语句之间不是孤立的,一个语句执行后的不同结果可能使另一个语句执行时得到不同的结果,或者决定了另一个语句执行或者不执行,这两种情况都称前一个语句影响了后一个语句。那么,当修改程序的某个部分(语句)时,可能潜在地影响到程序的其它部分     

一种基于前向计算的动态程序切片方法

动态程序切片技术是一种重要的程序分析技术,在软件分析、测试与调试过程中有着广泛的应用。给出一种基于前向计算的动态程序切片方法,该方法首先在对当前执行语句进行定义使用分析的基础上计算该语句定义变量的影响集,其次计算该语句的直接动态依赖关系,最后计算当前执行语句中变量的动态切片。根据该方法设计并实现了一个Java动态程序切片系统,基于一组基准测试程序开展了切片实验,并与已有的切片方法进行了比较。实验结果表明,该方法可以得到比较精确的动态程序切片结果。     

Oracle数据库中SQL语句的优化与分析

执行每个SQL语句,Oracle需要很多步骤.这些步骤中的每一步可能是从数据库中物理检索数据行,或者用某种方法准备数据行.Oracle用来执行语句的这些步骤的组合被称之为执行计划.执行计划是SQL优化中最为复杂也是最为关键的部分,只有知道了Oracle在内部到底是如何执行该SQL语句后,我们才能知道优化器选择的执行计划是否为最优的.     

基于Oracle数据库的SOL语句优化

通过分析Oracle数据库执行SQL语句的过程。采用比较SQL语句优化之前和优化之后的执行时间和调用的数据块数量方法来判断优化效果,最后得到消耗时间少和调用数据块少的SQL语句。     

基于数据库的语句优化经验之谈

该文是以Oracle数据库的语句为研究对象对象,由于其系统结构复杂,性能受多方面因素影响,其中SQL语句的执行效率是影响其性能的关键因素之一.所以该文将围绕SQL语句优化策略进行阐述,探讨如何设计最佳的SQL语句,提高SQL语句在数据库中的解析和执行效率,并给出了相关实例分析介绍.     

基于.Net平台分析SQL数据库操作C#语句

为了实现对SQL数据库的科学设计和开发,提高SQL数据库的运行性能,现针对.Net平台的使用特点,对SQL数据库操作中经常用到的C#语句进行总结和研究,同时,还从dataGridView的更新、条件查询语句两个方面入手,重点研究并测试了相关代码的使用性和延伸性.结果表明:给出的代码具有较高的使用价值,能够实现对SQL数据库的成功操作.     

基于关键谓词的程序错误定位方法

将程序切片技术应用于程序错误定位可以大量减少需要测试的语句数。提出一种基于关键谓词的程序错误定位方法,从程序中找出能影响输出结果的关键谓词,对该谓词和错误输出语句进行数据切片,并引入代码优先技术。该方法考虑了数据依赖和控制依赖,能实现准确快速的错误定位。     

A two-folded impact analysis of schema changes on database applications

Database applications are becoming increasingly popular, mainly due to the advanced data management facilities that the underlying database management system offers compared against traditional legacy software applications. The interaction, however, of such applications with the database system introduces a number of issues, among which, this paper addresses the impact analysis of the changes performed at the database schema level. Our motivation is to provide the software engineers of database applications with automated methods that facilitate major maintenance tasks, such as source code corrections and regression testing, which should be triggered by the occurrence of such changes. The presented impact analysis is thus two-folded： the impact is analysed in terms of both the affected source code statements and the affected test suites concerning the testing of these applications. To achieve the former objective, a program slicing technique is employed, which is based on an extended version of the program dependency graph. The latter objective requires the analysis of test suites generated for database applications, which is accomplished by employing testing techniques tailored for this type of applications. Utilising both the slicing and the testing techniques enhances program comprehension of database applications, while also supporting the development of a number of practical metrics regarding their maintainability against schema changes. To evaluate the feasibility and effectiveness of the presented techniques and metrics, a software tool, called DATA, has been implemented. The experimental results from its usage on the TPC-C case study are reported and analysed.     

Characterizing minimal semantics-preserving slices of function-linear, free, liberal program schemas

A program schema defines a class of programs, all of which have identical statement structure, but whose functions and predicates may differ. A schema thus defines an entire class of programs according to how its symbols are interpreted. As defined in this paper, a slice of a schema is obtained from a schema by deleting some of its statements. We prove that given a schema S which is function-linear, free and liberal, and a slicing criterion defined by the final value of a given variable after execution of any program defined by S, the minimal slice of S which respects this slicing criterion contains only the symbols ‘needed’ by the variable according to the data dependence and control dependence relations used in program slicing, which is the symbol set given by Weiser’s static slicing algorithm. Thus this algorithm gives minimal slices for programs representable by function-linear, free, liberal schemas. We also prove a similar result with termination behaviour used as a slicing criterion. This strengthens a recent result, in which S was required to be linear, free and liberal, and termination behaviour as a slicing criterion was not considered.     

Characterizing minimal semantics-preserving slices of predicate-linear, free, liberal program schemas

A program schema defines a class of programs, all of which have identical statement structure, but whose functions and predicates may differ. A schema thus defines an entire class of programs according to how its symbols are interpreted. A subschema of a schema is obtained from a schema by deleting some of its statements. We prove that given a schema S which is predicate-linear, free and liberal, such that the true and false parts of every if predicate satisfy a simple additional condition, and a slicing criterion defined by the final value of a given variable after execution of any program defined by S, the minimal subschema of S which respects this slicing criterion contains all the function and predicate symbols ‘needed’ by the variable according to the data dependence and control dependence relations used in program slicing, which is the symbol set given by Weiser’s static slicing algorithm. Thus this algorithm gives predicate-minimal slices for classes of programs represented by schemas satisfying our set of conditions. We also give an example to show that the corresponding result with respect to the slicing criterion defined by termination behaviour is incorrect. This complements a result by the authors in which S was required to be function-linear, instead of predicate-linear.     

Dynamic analysis of program performance (DAP) in a fortran batch environment

‘Frequency counts add an important new dimension to Fortran programs; indeed, it is difficult to express in words how “eye opening” they are’ (Knuth¹). Given a source program as input, a DAP environment effects changes to the execution of the program so that when the object code is run, the output of the program includes a list of the executable statements and their execution counts (a profile). By extending this basic principle so that the analysis also includes a time estimate for the statement (generated from the code associated with the statement) and a measure of the relative importance of the statement (with respect to the total run time of the object) the DAP report not only becomes an effective user software aid, but, also, an invaluable research tool. This paper discusses the development of such a DAP environment within a Fortran Batch System.     

Extracting reusable functions by flow graph based program slicing

An alternative approach to developing reusable components from scratch is to recover them from existing systems. We apply program slicing, a program decomposition method, to the problem of extracting reusable functions from ill structured programs. As with conventional slicing first described by M. Weiser (1984), a slice is obtained by iteratively solving data flow equations based on a program flow graph. We extend the definition of program slice to a transform slice, one that includes statements which contribute directly or indirectly to transform a set of input variables into a set of output variables. Unlike conventional program slicing, these statements do not include either the statements necessary to get input data or the statements which test the binding conditions of the function. Transform slicing presupposes the knowledge that a function is performed in the code and its partial specification, only in terms of input and output data. Using domain knowledge we discuss how to formulate expectations of the functions implemented in the code. In addition to the input/output parameters of the function, the slicing criterion depends on an initial statement, which is difficult to obtain for large programs. Using the notions of decomposition slice and concept validation we show how to produce a set of candidate functions, which are independent of line numbers but must be evaluated with respect to the expected behavior. Although human interaction is required, the limited size of candidate functions makes this task easier than looking for the last function instruction in the original source code     

向PE文件中插入代码技术的研究

PE文件格式是Windows操作系统引入的可执行文件格式。论文介绍windows平台下PE文件的基本结构。重点阐述了在不重编译源码的前提下实现代码插入技术所涉及的基本任务:把代码插入到PE文件中可用的空闲空间或者在文件尾部添加一个新的节来插入代码;如何用一般方法钩住程序的控制和和重定位插入代码;插入代码如何获取对其有用的windowsAPI函数的地址。向PE文件插入外部代码技术的研究是很有价值的,它对反PE型病毒和软件加壳技术的研究都很有用。     

失效上下文统计分析的软件故障定位方法

针对程序切片方法不提供语句的可疑程度描述,而覆盖分析方法不能充分分析程序元素间的相互影响等问题,提出上下文统计分析的软件故障定位方法。首先,将源程序转换为抽象语法树和程序依赖图;接下来,插桩程序,收集运行时信息;然后,根据失效点,执行按需的反向动态切片,确定失效产生的上下文;最后,对于反向动态切片中的节点,统计计算可疑度,输出带可疑度排序的动态程序切片。该方法不但描述了失效产生的上下文,还计算上下文中各个语句的可疑度。实验结果表明,所提方法与单一的覆盖分析方法相比,平均Expense降低了1.3%,与单一的切片方法相比,平均Expense降低了5.6%,所提方法可以有效辅助开发人员定位与修正软件缺陷。     

一种基于分层切片模型思想的源程序信息分析方案

作为软件理解的手段之一,程序切片技术通过寻找程序内部的相关性来分解程序,再通过对分解所得程序切片的分析达到对整个程序的分析和理解。程序切片算法必须建立在对源程序信息正确、完整分析的基础上。详细地描述了一种基于分层切片模型思想的程序信息提取方案。该方案已成功运用到一种Java程序切片工具模型JSTM（Java Slicing Tools Model)中。