Understanding Oracle Clusterware in High Availability Architecture

 RoadToMaster –  Oracle Clusterware enables servers to communicate with each other, so that they appear to function as a collective unit. Oracle Clusterware provides the infrastructure necessary to run Oracle Real

Application Clusters (Oracle RAC) and Oracle RAC One Node. The Grid Infrastructure is the software that provides the infrastructure for an enterprise grid architecture. In a cluster, this software includes Oracle Clusterware and Oracle ASM. For a standalone server, the Grid Infrastructure includes Oracle Restart and Oracle ASM. Oracle Database 11g Release 2 combines these infrastructure products into one software installation called the Grid Infrastructure home.

Oracle Clusterware, as part of Oracle Grid Infrastructure, is software that manages the availability of user applications and Oracle databases. Oracle Clusterware is the only clusterware needed for most platforms on which Oracle RAC operates. You can also use clusterware from other vendors in addition to Oracle Clusterware on the same system, if needed. However, adding unnecessary layers of software for functionality that is provided by Oracle Clusterware adds complexity and cost and can reduce system availability, especially for planned maintenance.

Understanding Automatic Storage Management (ASM)

RoadToMaster – Automatic Storage Management (ASM) is an integrated, high-performance database file system and disk manager. ASM is based on the principle that the database should manage storage instead of requiring an administrator to do it. ASM eliminates the need for you to directly manage potentially thousands of database files.

ASM groups the disks in your storage system into one or more disk groups. You manage a small set of disk groups and ASM automates the placement of the database files within those disk groups.

ASM provides the following benefits:

Understanding Oracle Database High Availability (HA) Solutions

  RoadToMaster –  Oracle Database offers an integrated suite of high availability solutions that increase availability and eliminate or minimize both planned and unplanned downtime. These solutions also help enterprises maintain business continuity 24 hours a day, seven days a week.

1.  Oracle Real Application Clusters (RAC)

Oracle Real Application Clusters (RAC) allows Oracle  Database to run any packaged or custom application unchanged across a set of clustered servers. This capability provides the highest levels of availability and the most flexible scalability. If a clustered server fails, Oracle Database continues running on the surviving servers. When more processing power is needed, you can add another server without interrupting access to data.

Understanding Common Causes Oracle DB Downtime

 RoadToMaster –  Availability is the degree to which an application, service, or functionality is available upon demand. Availability is measured by the perception of an application’s end user. End users experience frustration when their data is unavailable, and they do not understand or care to differentiate between the complex components of an overall solution. Performance failures due to higher than expected usage create the same havoc as the failure of critical components in the solution. And . Both small businesses and global enterprises have users al lover the world who require access to data 24 hours a day.

Reliability, recoverability, timely error detection, and continuous operations are primary characteristics of a highly available solution:

Understanding Oracle Initialization Parameter Files

  RoadToMaster –  When you start the instance, an initialization parameter file is read.  There are two types of parameter files:

 Server parameter file: This is the preferred type of initialization parameter file. It is a binary file that can be written to and read by the database server and must not be edited manually. It resides in the server that the Oracle database is executing on, and is persistent across shutdown and startup. This is often referred to as a server parameter file (SPFILE). The default name of this file, which is automatically sought at startup, is spfile<SID>.ora.

Text initialization parameter file: This type of initialization parameter file can be read by the database server, but it is not written to by the server. The initialization parameter settings must be set and changed manually by using a text editor so that they are persistent across shutdown and startup. The default name of this file, which is automatically sought at startup if an SPFILE is not found, is init<SID>.ora.

It is recommended that you create an SPFILE as a dynamic means of maintaining initialization parameters. By using an SPFILE, you can store and manage your initialization parameters persistently in a server-side disk file.

Creating an Oracle Database 10g Manually

RoadToMaster – This section presents the steps involved when you create a database manually. These steps should be followed in the order presented. The prerequisites described in the preceding section must already have been completed. That is, you have established the environment for creating your Oracle Database, including most operating system dependent environmental variables, as part of the Oracle software installation process.

Step 1: Decide on Your Instance Identifier (SID)
Step 2: Establish the Database Administrator Authentication Method
Step 3: Create the Initialization Parameter File
Step 4: Connect to the Instance
Step 5: Create a Server Parameter File (Recommended)
Step 6: Start the Instance
Step 7: Issue the CREATE DATABASE Statement
Step 8: Create Additional Tablespaces
Step 9: Run Scripts to Build Data Dictionary Views
Step 10: Run Scripts to Install Additional Options (Optional)
Step 11: Back Up the Database.

The examples shown in these steps create an example database mynewdb.

Creating an Oracle Database 10g via DBCA

Planning the Database

As a DBA, you must plan:
1. The logical storage structure of the database and its physical implementation:
* How many disk drives do you have for this?
* How many data files will you need? (Plan for growth.)
* How many tablespaces will you use?
* Which type of information will be stored?
* Are there any special storage requirements due to type or size?
2. The overall database design
3. A backup strategy for the database

Oracle 10g Database Structure

RoadToMaster – Each running Oracle database is associated with an Oracle instance. When a database is started on a database server, the Oracle software allocates a shared memory area called the System Global Area (SGA) and starts several Oracle background processes. This combination of the SGA and the Oracle processes is called an Oracle instance.

After starting an instance, the Oracle software associates the instance with a specific database. This is called mounting the database. The database is then ready to be opened, which makes it accessible to authorized users. Multiple instances can execute concurrently on the same computer, each accessing its own physical database.

You can look at the Oracle database architecture as various interrelated structural components.

An Oracle database uses memory structures and processes to manage and access the database. All memory structures exist in the main memory of the computers that constitute the database server. Processes are jobs that work in the memory of these computers. A process is defined as a “thread of control” or a mechanism in an operating system that can run a series of steps.

Database Structures consist of  Memory Structure, Process Structure, and Storage Structure

Oracle 10g Architecture

RoadToMaster – Basically, there are two main components of Oracle database –– instance and database itself. An instance consists of some memory structures and the background processes, whereas a database refers to the disk resources. Figure 1 will show you the relationship.

Instance

As we cover above, the memory structures and background processes contitute an instance. The memory structure itself consists of System Global Area (SGA), Program Global Area (PGA), and an optional area –– Software Area Code. In the other hand, the mandatory background processes are Database Writer (DBWn), Log Writer (LGWR), Checkpoint (CKPT), System Monitor (SMON), and Process Monitor (PMON). And another optional background processes are Archiver (ARCn), Recoverer (RECO), etc. Figure 2 will illustrate the relationship for those components on an instance.