Working with SQL and PL/SQL/ Session 1 / 1 of 27 SQL Server Architecture

Working with SQL and PL/SQL/ Session 1 / 1 of 27

SQL Server Architecture


Objective

Relational Database Components Database Architecture Logical Database Components System Databases and Data Physical Database Architecture Physical Database Files and Filegroups Transaction Log Architecture


Introduction

In 1980’s Microsoft & Sybase teamed up to create SQL Server.

After release of version 6.5, they both separated.

It is SQL – compliant RDBMS. ( Uses ANSI version of SQL)

It supports the Client Server Model.


Relational features of SQL Server

Information representation. Unique definition of rows. Systematic treatment of NULL values. Guaranteed access High level Update, Insert and Delete. Security

Login authentication Permissions validation on user database.


Relational Database Components

The database component of Microsoft SQL Server 2000 is a Structured Query Language (SQL)–based, scalable, relational database with integrated Extensible Markup Language (XML) support for Internet applications.

Each of the following terms describes a fundamental part of the architecture of the SQL Server 2000 database component:


Database

A database is a storage place for data. The database does not present information directly to a user; the user runs an application that accesses data from the database and presents it to the user in an understandable format.

A database typically has two main parts: first, the files holding the physical database and second, the database management system (DBMS) software that applications use to access data.


The DBMS is responsible for enforcing the database structure, including:

Maintaining relationships between data in the database.

Ensuring that data is stored correctly, and that the rules defining data relationships are not violated.

Recovering all data to a point of known consistency in case of system failures.


Scalable

SQL Server 2000 supports having a wide range of users access it at the same time. An instance of SQL Server 2000 includes the files that make up a set of databases and a copy of the DBMS software.

Applications running on separate computers use a SQL Server 2000 communications component to transmit commands over a network to the SQL Server 2000 instance.


Structured Query Language

To work with data in a database, you have to use a set of commands and statements (language) defined by the DBMS software ; the most common is SQL.

The American National Standards Institute (ANSI) and the International Standards Organization (ISO) define software standards, including standards for the SQL language.


The dialect of SQL supported by Microsoft SQL Server is called Transact-SQL (T-SQL). T-SQL is the primary language used by Microsoft SQL Server applications.

Elements of Transact SQL: DDL DML DCL TCL


Extensible Markup Language

Although most SQL statements return their results in a relational, or tabular, result set, the SQL Server 2000 database component supports a FOR XML clause that returns results as an XML document. XML documents can be added to SQL Server databases, and the OPENXML clause can be used to expose data from an XML document as a relational result set.


Database Architecture

Microsoft® SQL Server™ 2000 data is stored in databases. The data in a database is organized into the logical components visible to users. A database is also physically implemented as two or more files on disk.

When using a database, you work primarily with the logical components such as tables, views, procedures, and users. The physical implementation of files is largely transparent.


Each instance of SQL Server has four system databases (master, model, tempdb, and msdb) and one or more user databases.

It is not necessary to run multiple copies of the SQL Server database engine to allow multiple users to access the databases on a server.

An instance of the SQL Server Standard or Enterprise Edition is capable of handling thousands of users working in multiple databases at the same time.


Logical Database Components The data in a Microsoft SQL Server 2000

database is organized into several different objects.

Tables Constraints Indexes Defaults Triggers, Stored procedures, Views Keys User-defined functions User-defined data types


Physical Database Architecture

The fundamental unit of data storage in Microsoft SQL Server is the page. In SQL Server 2000, the page size is 8 KB.

The start of each page is a 96-byte header used to store system information, such as the type of page, the amount of free space on the page, and the object ID of the object owning the page


Continued.. Data pages contain all the data in data

rows except text, ntext, and image data, which is stored in separate pages.

Data rows are placed serially on the page starting immediately after the header.

A row offset table starts at the end of the page. The row offset table contains one entry for each row on the page and each entry records how far the first byte of the row is from the start of the page.


Rows cannot span pages in SQL Server. In SQL Server 2000, the maximum amount of data contained in a single row is 8060 bytes, not including text, ntext, and image data

Extents are the basic unit in which space is allocated to tables and indexes. An extent is 8 contiguous pages, or 64 KB.


Physical Database Files and Filegroups SQL Server 2000 databases have three types

of files:

1. Primary data files This file contains all of the system tables

and other system objects. Also contains links to all secondary data files & log files.

Microsoft recommends that most databases will work very well with only a single primary data file & log file.

The recommended file name extension for primary data files is .mdf.


2. Secondary data files Secondary data files comprise all of the

data files other than the primary data file. Some databases may not have any secondary data files, while others have multiple secondary data files.

Used to spread data over multiple disks. The recommended file name extension

for secondary data files is .ndf.


3. Log files Log files hold all of the log information

used to recover the database. There must be at least one log file for each database, although there can be more than one.

If the server fails because of a power outage or other problem, SQL Server automatically recovers the database by applying committed transactions.

The recommended file name extension for log files is .ldf.


SQL Server 2000 files have two names: 1. logical_file_name is a name used to refer

to the file in all Transact-SQL statements. The logical file name must conform to the

rules for SQL Server identifiers and must be unique to the database.

2. os_file_name is the name of the physical file. It must follow the rules for Microsoft Windows

NT or Microsoft Windows 98, and Microsoft Windows 95 file names.


Database Filegroups

Database files can be grouped together in filegroups for allocation and administration purposes.

Some systems can improve their performance by controlling the placement of data and indexes onto specific disk drives.

The administrator can create filegroups for each disk drive, then assign specific tables, indexes, or the text, ntext, or image data from a table, to specific filegroups.


There are two types of filegroups: 1. Primary

The primary filegroup contains the primary data file and any other files not specifically assigned to another filegroup. All pages for the system tables are allocated in the primary filegroup.

2. User-defined User-defined filegroups are any filegroups

specified using the FILEGROUP keyword in a CREATE DATABASE or ALTER DATABASE statement.


One filegroup in each database operates as the default filegroup. When SQL Server allocates a page to a table or index for which no filegroup was specified when they were created, the pages are allocated from the default filegroup.

Only one filegroup at a time can be the default filegroup. If no default filegroup is specified, the primary filegroup is the default filegroup.


The Syntax:

CREATE DATABASE database_name[ ON [ PRIMARY] ( [ <filespec> ……] ) [ LOG ON ] ( [ <filespec …..] )]


Creating Database

CREATE DATABASE MyDBON PRIMARY ( NAME='MyDB_Primary', FILE NAME= 'c:\data\

MyDB_Prm.mdf', SIZE=4, MAXSIZE=10, FILEGROWTH=1)


LOG ON ( NAME='MyDB_log', FILE NAME = 'c:\data\MyDB.ldf', SIZE=1, MAXSIZE=10, FILEGROWTH=1)

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Working with SQL and PL/SQL/ Session 1 / 1 of 27 SQL Server Architecture