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In addition to free Oracle DBA Tutorials, we will cover common interview questions, issues and how to’s of Oracle DBA.
An Oracle database is a collection of data treated as a unit. The purpose of a database is to store and retrieve related information. A database server is the key to solving the problems of information management. In general, a server reliably manages a large amount of data in a multi user environment so that many users can concurrently access the same data. All this is accomplished while delivering high performance. A database server also prevents unauthorized access and provides efficient solutions for failure recovery.
Oracle Database is the first database designed for enterprise grid computing, the most flexible and cost effective way to manage information and applications. Enterprise grid computing creates large pools of industry-standard, modular storage and servers. With this architecture, each new system can be rapidly provisioned from the pool of components. There is no need for peak workloads, because capacity can be easily added or reallocated from the resource pools as needed.
The database has logical structures and physical structures. Because the physical and logical structures are separate, the physical storage of data can be managed without affecting the access to logical storage structures.
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A 64-bit Linux version of Oracle will not install on a 32-bit Linux or Windows 64-bit system, for example. The Oracle release notes provide information about where to find the compatibility matrix and the system requirements for the server.
The disk space requirements depend on the components installed, but the base product alone does require more disk space for 64-bit operating systems. You can use the following command-line option to run the installer with parameters to perform just the system prerequisites checks, without continuing to install Oracle:
E:\Oracle11gR2\database> setup.exe –executeSysPrereqs
The results can be viewed in the prerequisite_results.xml file, which will be in the oraInventory/logs directory.
SQL Server tends to have a default location for the binaries, and Oracle will set up a default as well: the Oracle home directory. This directory location can be set during the installation process, or it can be specified by setting the ORACLE_HOME environment variable before running the installer.
Although the environment variables are set by the Oracle installer for Windows, there might be more than one Oracle home on a server. If this is the case, when using a command line, you will need to set the variable ORACLE_HOME first, or fully qualify the path to the correct Oracle home.
C:\> set ORACLE_HOME=d:\oracle\product\11.2.0\db_1
C:\> set ORACLE_SID=orcl
User Account for Installation
The installer creates the ORA_DBA group automatically on the Windows platform. A standard practice with SQL Server is to create another user that has administrator privileges to install the software and be the owner of the SQL Server services.
By default, the Oracle services will use the Local Service account. By having a separate domain account to manage these services and perform the installation.
The database software should be installed on the NTFS file system because of the security available for the Oracle home directory, which will contain trace files and database files.
Database is not really meant to be a stand-alone machine, it needs network connectivity. Clustering will have different requirements, but the database server needs to have a primary IP address that is accessible (it doesn’t need to be a static IP, unless your environment requires that
If you are using a dynamic configuration (DHCP), a test conducted during the Oracle installer’s prerequisite check will fail if Microsoft Loopback Adapter is not the primary network adapter on the system. Here is a quick check for this adapter:
C:\> ipconfig /all Ethernet adapter Local Area Connection 2: Connection-specific DBS Suffix . . . . : Description . . . . . . . . . . . . . .: Microsoft Loopback Adapter Physical Address . . . . . . . . . . . : 7A-80-4C-9F-57-5D DHCP Enabled . . . . . . . . . . .. . .: Yes Autoconfiguration Enabled . . . . . . .: Yes
If Microsoft Loop back Adapter is not configured, you can set it up through Add/Remove Hardware in the Control Panel. Select Network Adapters, and add it as a new network adapter.
Windows Platform Checklist:-
For Windows installations:
-Check that the operating system version and Oracle version and edition are correct.
-Verify that the hardware requirements are met.
-Create an Oracle account with administrator permissions to perform the installation.
-Run the prerequisite check and correct any issues found.
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The following are some other useful Linux commands:
-pwd Shows the current directory.
-echo $ORACLE_HOME Shows the value of the variable.
-whoami Shows the current user.
-ps -ef Shows the list of current processes running on the server.
-grep Searches for a name or value in a file or list or process.
-chmod Changes permissions for a file or directory.
-chgrp Changes the group for permissions of a file or directory.
-chown Changes the owner of a file or directory.
The manual pages (man pages) provide parameter options and examples of how to use the commands. To access the man page for a command, just type man and the command at the prompt, as in this example:
> man grep
When you download files for a Linux system, such as patches or software, they might come in a couple of formats, with file names ending in .Z, .gz, .zip, .cpio, or .tar. These are compressed files. You’ll need to uncompress these files so that they are usable. The following are sample commands to uncompress the various formats:
> uncompress *.Z
> unzip *.zip
> gunzip *.gz
> tar -xvf file.tar
> cpio -idmv < file_name
For a Linux system, you need to set up users, adjust permissions and kernel parameters, and make sure the required packages are installed.
Overview of Oracle Grid Architecture
Grid computing is a new IT architecture that produces more resilient and lower cost enterprise information systems. With grid computing, groups of independent, modular hardware and software components can be connected and rejoined on demand to meet the changing needs of businesses.
The grid style of computing aims to solve some common problems with enterprise IT: the problem of application silos that lead to under utilized, dedicated hardware resources, the problem of monolithic, unwieldy systems that are expensive to maintain and difficult to change, and the problem of fragmented and disintegrated information that cannot be fully exploited by the enterprise as a whole.
Overview of Application Architecture
There are two common ways to architect a database: client/server or multitier. As internet computing becomes more prevalent in computing environments, many database management systems are moving to a multitier environment.
Client/Server ArchitectureMultiprocessing uses more than one processor for a set of related jobs. Distributed processing reduces the load on a single processor by allowing different processors to concentrate on a subset of related tasks, thus improving the performance and capabilities of the system as a whole.
An Oracle database system can easily take advantage of distributed processing by using its client/server architecture. In this architecture, the database system is divided into two parts: a front-end or a client, and a back-end or a server.
The client is a database application that initiates a request for an operation to be performed on the database server. It requests, processes, and presents data managed by the server. The client workstation can be optimized for its job. For example, it might not need large disk capacity, or it might benefit from graphic capabilities.
Often, the client runs on a different computer than the database server, generally on a PC. Many clients can simultaneously run against one server.
The server runs Oracle software and handles the functions required for concurrent, shared data access. The server receives and processes the SQL and PL/SQL statements that originate from client applications. The computer that manages the server can be optimized for its duties. For example, it can have large disk capacity and fast processors.
Multitier Architecture: Application Servers
A multitier architecture has the following components:
-A client or initiator process that starts an operation
-One or more application servers that perform parts of the operation. An application server provides access to the data for the client and performs some of the query processing, thus removing some of the load from the database server. It can serve as an interface between clients and multiple database servers, including providing an additional level of security.
-An end or database server that stores most of the data used in the operation
This architecture enables use of an application server to do the following:
-Validate the credentials of a client, such as a Web browser
-Connect to an Oracle database server
-Perform the requested operation on behalf of the client
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