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It supports multiple processes and provides concurrency control. Each process has direct, efficient access to the data. In all cases, stored data is ultimately contained in structures known as globals a later section in this chapter discusses these. Routines and classes can call each other.
Classes provide object-oriented features. Database storage is an integrated part of all Cache programming languages. Classes can persist data in a way that simplifies programming. If you use persistent classes, data is simultaneously available as objects, SQL tables, and globals. You can access globals directly from either routines or classes, which means that you have the flexibility to store and access data exactly how you want.
In contrast, some newer applications are written almost entirely in classes. You can choose the approach that is appropriate for your needs. It includes commands, functions, and operators that are used in the various MultiValue implementations, and it supports multiple emulation modes so that you can use syntax that is familiar to you. The next chapter provides an introduction to ObjectScript.
You can use the system classes and you can define your own classes. It can also include items not usually defined in classes, including triggers, queries, and indices. The following shows a class definition: Class Sample. The default is ObjectScript; the next chapter provides an introduction to it. There are additional options for client-side programming, not discussed in this book.
You can use classes from within routines. For example, the following shows part of a routine, in which we refer to the Sample. Name write! Age write!
The next chapter introduces these more thoroughly; for now, it is important just to know the following points: A global consists of a set of nodes in some cases, only one node , identified by subscripts. Each node can contain a value. A global is automatically stored in the database.
When you assign a value to a node of a global variable, the data is written immediately to the database. You can see the contents of a global via an ObjectScript command or via the Management Portal. At the lowest level, all access to data is done via direct global access — that is, by using commands and functions that work directly with globals. Some of these applications use direct global access. These APIs, of course, internally use direct global access.
Internally, the system always uses direct global access. You can do so, if you understand the structure of the globals. These optimizations ensure that operations on globals have high throughput number of operations per unit of time , high concurrency total number of simultaneous users , efficient use of cache memory, and require no ongoing performance-related maintenance such as frequent rebuilding, re-indexing, or compaction.
The physical structure used to store globals is completely encapsulated; it is generally unnecessary to consider the physical data structure.
Global storage is sparse, meaning that only nodes with data values are stored in the database. Other benefits of globals include the following: The hierarchical structure of globals typically models real-world data more closely than is possible with relational tables. The sparse nature means that new fields can be added without any overhead and without rebuilding the existing database. Macros ObjectScript also supports macros, which define substitutions.
The definition can either be a value, an entire line of code, or with the Continue directive multiple lines. You use macros to ensure consistency. For example: define StringMacro "Hello, World!
It also refers to another macro. You can use macros in routines as well as in classes. Some of the system classes use them extensively. Include Files You can define macros in a routine and use them later in the same routine. More commonly, you define them in a central place.
To do this, you create and use include files. An include file defines macros and can include other include files. That routine can refer to the macros defined in the include file.
Include the include file at the start of any class. Methods in that class can refer to the macros. Include the include file at the start of any method. That method can refer to the macros. Note that you use slightly different syntax to include an include file within a class definition. There are multiple steps; the preceding figure gives a general idea of them. It is not necessary to know the steps in detail, but the following points are good to remember: The CSP engine converts CSP files into class definitions.
In some cases, the compiler first uses classes as the basis for generating and saving additional classes. You can look at these classes in Studio, but do not modify them. This occurs, for example, when you compile classes that define web services and web clients. The class compiler also generates the class descriptor for each class.
The system code uses this at runtime. A preprocessor sometimes called the macro preprocessor or MPP uses the include files not shown in the figure and replaces the macros. These changes occur in a temporary work area, and your code is not changed. This layer is known as intermediate code.
In this layer, all access to the data is done via direct global access. A later section of this book shows you how to find this code, which can be useful for diagnostic purposes. After you compile your classes, you can put them into deployed mode. This fact makes the code easier to manage.
Introduction to Caché Programming
Click Download or Read Online button to get cach objectscript and mumps book now. This site is like a library, Use search box in the widget to get ebook that you want. It is designed as both a comprehensive learning guide and a technical reference manual. It then progresses on to System-Supplied Functions.
Cache ObjectScript and MUMPS : Technical Learning Manual