14261_4 SQL Server 2008 Databses

8/3/2019 14261_4 SQL Server 2008 Databses

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SQL Server 2008 Databases


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Types of databases

1. System Databases: used to store system wide

data and metadata.

2. User Databases: Created by users who havethe appropriate level ofpermissions to store

application data.


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System Databases

System database Description

master Database Records all the system-level information for an instance of SQL

Server.

msdb Database Is used by SQL Server Agent for scheduling alerts and jobs.

model Database Is used as the template for all databases created on the instance of

SQL Server. Modifications made to the model database, such as

database size, collation, recovery model, and other database

options, are applied to any databases created afterward.

Resource Database Is a read-only database that contains system objects that are

included with SQL Server. System objects are physicallypersisted in

the Resource database, but they logically appear in the sys schemaof every database.

tempdb Database Is a workspace for holding temporary objects or intermediate result

sets.


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Master Database

The master database records all the system-levelinformation for a SQL Server system. This includes instance-wide metadata such as logon accounts, endpoints, linkedservers, and system configuration settings.

master is the database that records the existence of allother databases and the location of those database filesand records the initialization information for SQL Server.Therefore, SQL Server cannot start if the master database isunavailable.

In SQL Server, system objects are no longer stored inthe masterdatabase; instead, they are stored inthe Resource database.


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Model Database

The model database is used as the template for alldatabases created on an instance of SQL Server.Because tempdb is created every time SQL Server isstarted, the modeldatabase must always exist on a SQL

Server system. When a CREATE DATABASE statement is issued, the first

part of the database is created by copying in the contentsof the model database. The rest of the new database isthen filled with emptypages.

Ifyou modify the model database, all databases createdafterward will inherit those changes. For example, youcould set permissions or database options, or add objectssuch as tables, functions, or stored procedures.


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MSDB Database

It is considered as the sql server agents databaseas it is responsible for all automated andscheduled operations(i.e. used extensively for the

storage of automated job definitions, jobschedules, operator definitions, and alertdefinitions)

It is also used by service broker, database mail,

Reporting services. For storage of SSIS packages ,it is also used by

integration services


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tempdb database

The tempdb system database is a global resource that isavailable to all users connected to the instance of SQLServer Operations

tempdb is re-created every time SQL Server is started so

that the system always starts with a clean copy of thedatabase.

Temporary tables and stored procedures are droppedautomatically on disconnect, and no connections are activewhen the system is shut down.

Backup and restore operations are not allowed on tempdb.

The size oftempdb can affect the performance of a system.overhead with the growing database can be avoided byincreasing the size oftempdb.


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Used by sql server to store temporary objects(i.e.temporary tables, views,cursors and table valuedvariables)

Stores work tables containing intermediate results of aqueryprior to a sort opeartion or any other

manipulation(sorting operation would be performed in itand return sorted results)

Used to support connection options.

It used to hold the following: Temporary user objects that are explicitly created i.e. temp

tables, stored procedures, variables, or cursors. Internal objects that are created by the SQL Server Database

Engine, for example, work tables to store intermediate resultsfor spools or sorting.

Etc


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Resource Database

The Resource database is a read-only database that contains all thesystem objects that are included with SQL Server.

SQL Server system objects, such as sys.objects, are physicallypersisted in the Resource database, but they logically appear in thesys schema of every database.

The Resource database does not contain user data or usermetadata.

The Resource database makes upgrading to a new version of SQLServer an easier and faster procedure.

In earlier versions of SQL Server, upgrading required dropping and

creating system objects. Because the Resource database filecontains all system objects, an upgrade is now accomplished simplyby copying the single Resource database file to the local server.

It is not accessible during normal database operations.


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The physical file names of the Resource database aremssqlsystemresource.mdf and mssqlsystemresource.ldf. These filesare located in :\Program Files\Microsoft SQLserver\MSSQL10_50.\MSSQL\Binn\. Each instanceof SQL Server has one and only one associatedmssqlsystemresource.mdf file, and instances do not share this file.

SQL Server cannot back up the Resource database.

The Resource database should only be modified by or at thedirection of a Microsoft Customer Support Services (CSS) specialist.

The ID of the Resource database is always 32767.

Other important values associated with the Resource database arethe version number and the last time that the database wasupdated.


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Distribution Databases

It stores metadata and transactional history tosupport all types of replication on a SQL server

One database distribution is sufficient.However if

needed,multiple distribution databases can beconfigured.

A model distribution database is installed bydefault and is used in the creation of a

distribution database used in replication.

It is installed in the same location as the rest ofthe system databases and is named distmdl.mdf


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SQL Server 2008 Database Storage

Two files to store all system and user

databases(including the resource db)-

Data File (Default extension is .mdf)

Transaction log file(Default extension is .ldf)

The default location for the system db files is

:\Program Files\Microsoft SQL

Server\MSSQL.X\MSSQL\Datahere x is the instance number

Only developer can manipulate system databases


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Documents

14261_4 SQL Server 2008 Databses