Program Global Area (PGA)

Program Global Area Components The Program Global Area or Process Global Area (PGA) is a memory region that contains data and control information for a single server process or a single background process. The PGA is allocated when a process is created and deallocated when the process is terminated. In contrast to the SGA, which is shared by several processes, the PGA is an area that is used by only one process. Content of the PGA The content of the PGA memory varies, depending...

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SGA_TARGET Initialization Parameter

SGA_TARGET specifies the total size of all SGA components. If SGA_TARGET is specified, then the following memory pools are automatically sized: Buffer cache (DB_CACHE_SIZE) Shared pool (SHARED_POOL_SIZE) Large pool (LARGE_POOL_SIZE) Java pool (JAVA_POOL_SIZE) Streams pool (STREAMS_POOL_SIZE) If these automatically tuned memory pools are set to non-zero values, then those values are used as minimum levels by Automatic Shared Memory Management. You would set minimum values if an application component needs a minimum amount of memory to function...

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SGA_MAX_SIZE Initialization Parameter

Oracle Database can set limits on how much virtual memory the database uses for the SGA. It can start instances with minimal memory and allow the instance to use more memory by expanding the memory allocated for SGA components, up to a maximum determined by the SGA_MAX_SIZE initialization parameter. If the value for SGA_MAX_SIZE in the initialization parameter file or server parameter file (SPFILE) is less than the sum the memory allocated for all components, either explicitly in the parameter file or by default, at the time the instance is initialized,...

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Dynamic SGA and SGA Granules

A dynamic SGA implements an infrastructure that allows the SGA configuration to change without shutting down the instance. With the dynamic SGA infrastructure, the size of the buffer cache, the shared pool, the large pool, and the process-private memory can be changed without shutting down the instance. Oracle can start instances underconfigured and allow the instance to use more memory by growing the SGA components, up to a maximum of SGA_MAX_SIZE. If SGA_MAX_SIZE specified in the initialization parameter file is less than the sum of all...

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System Global Area (SGA)

 The System Global Area (SGA) is a group of shared memory areas that are dedicated to an Oracle instance. All Oracle processes use the SGA to hold information. The SGA is used to store incoming data and internal control information that is needed by the database. You control the amount of memory to be allocated to the SGA by setting some of the Oracle  initialization parameters. An SGA and Oracle processes constitute an Oracle instance. Oracle automatically allocates memory for an SGA...

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Instance Memory Structure

The size of these structures affects the performance of the Oracle database server and is controlled by initialization parameters. These initialization parameters can be categorized as memory parameters. When a database is created with DBCA, the memory parameters are automatically set to optimal values based on your specification of the database workload. However, as your database usage expands, you might find it necessary to alter the settings of the memory parameters. Oracle provides alerts and...

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Setting Initial Database ArchiveLog Mode

You set the initial archiving mode as part of database creation in the CREATE DATABASE statement. Usually, you can use the default of NOARCHIVELOG mode at database creation because there is no need to archive the redo information generated by that process. After creating the database, decide whether to change the initial archiving mode. If you specify ARCHIVELOG mode, you must have initialization parameters set that specify the destinations for the archive log files Changing the Database Archiving Mode To change the archiving mode of the database,...

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ArchiveLog Mode

When you run a database in ARCHIVELOG mode, you enable the archiving of the redo log. The database control file indicates that a group of filled redo log files cannot be reused by LGWR until the group is archived. A filled group becomes available for archiving immediately after a redo log switch occurs. The archiving of filled groups has these advantages: A database backup, together with online and archived redo log files, guarantees that you can recover all committed transactions in the event of an operating system or disk failure.  If you...

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NoArchiveLog Mode

When you run your database in NOARCHIVELOG mode, you disable the archiving of the redo log. The database control file indicates that filled groups are not required to be archived. Therefore, when a filled group becomes inactive after a log switch, the group is available for reuse by LGWR. NOARCHIVELOG mode protects a database from instance failure but not from media failure. Only the most recent changes made to the database, which are stored in the online redo log groups, are available for instance recovery. If a media failure occurs while the...

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NoArchiveLog Mode and ArchiveLog Mode

You set the initial archiving mode as part of database creation in the CREATE DATABASE statement. Usually, you can use the default of NOARCHIVELOG mode at database creation because there is no need to archive the redo information generated by that process. After creating the database, decide whether to change the initial archiving mode.If you specify ARCHIVELOG mode, you must have initialization parameters set that specify the destinations for the archive log files.This section describes the issues you must consider when choosing to run your database...

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Archived Redo Logs Files

What Is the Archived Redo Log? Oracle Database lets you save filled groups of redo log files to one or more offline destinations, known collectively as the archived redo log, or more simply the archive log. The process of turning redo log files into archived redo log files is called archiving. This process is only possible if the database is running in ARCHIVELOG mode. You can choose automatic or manual archiving.An archived redo log file is a copy of one of the filled members of a redo log group....

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Logical Storage Structure

Oracle Database allocates logical space for all data in the database. The logical units of database space allocation are data blocks, extents, segments, and tablespaces. At a physical level, the data is stored in data files on disk. The data in the data files is stored in operating system blocks. The logical parts of the Oracle database are those structures within Oracle that determine where in the physical structures your table and index data reside. Since at the core of every operating system...

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Physical Storage Structure

The physical structure of an Oracle database is determined by the operating system files that provide the actual physical storage for database information.One characteristic of an RDBMS is the independence of logical data structures such as tables, views, and indexes from physical storage structures. Because physical and logical structures are separate, you can manage physical storage of data without affecting access to logical structures. For example, renaming a database file does...

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Database Storage Structure

An Oracle database is made up of physical and logical structures. Physical structures are those that can be seen and operated on from the operating system, such as the physical files that store data on a disk. Logical structures are created and recognized by Oracle Database and are not known to the operating system. The primary logical structure in a database, a tablespace, contains physical files. The applications developer or user may be aware of the logical structure, but is not usually aware of this physical structure. The DBA must understand...

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Oracle Database

Oracle introduced the first commercial Relational Database Management System (RDBMS) almost 30 years ago. Oracle database consists of operating system files, also known as database files, that provide the actual physical storage for database information. The database files are used to ensure that the data is kept consistent and can be recovered in the event of a failure of the instance. The general purpose of a database is to store and retrieve related information. An Oracle database...

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How to Become a Database Administrator

While searching jobs some people go for database administrator but not many people know how to become a database administrator. When we talk about a particular job, it is necessary to know what the job is about and its prospect in future. Before the implantation of computers and laptops in one word electronic gadgets, data of office, schools, industry, factory and other places were recorded in note books. This particular process was quite length and time consuming...... Even it was very difficult...

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Database Adminstrator

In this new era of information technology, data and information is central and a key aspect of any company’s business activities. This data and information must be logged, backed-up, protected but most importantly easily available for staff to use to make crucial business decisions. As a result, there must be people in charge of managing this data and these people are called database administrators.A database administrator (short form DBA) is a person responsible for the design, implementation,...

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Introduction to an Oracle Instance

Every running Oracle database is associated with an Oracle instance. When a database is started on a database server (regardless of the type of computer), Oracle allocates a memory area called the System Global Area (SGA) and starts one or more Oracle processes. This combination of the SGA and the Oracle processes is called an Oracle instance. The memory and processes of an instance manage the associated database's data efficiently and serve the one or multiple users of the database.An instance...

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Database Management System (DBMS)

DBMS means "Database Management System."A DBMS is a set of software programs that controls the system organization, storage, management, and retrieval of data in a database. DBMSs are categorized according to their data structures or types. The DBMS accepts requests for data from an application program and instructs the operating system to transfer the appropriate data. The queries and responses must be submitted and received according to a format that conforms to one or more applicable protocols. When a DBMS is used, information systems can be...

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What is Database

A database is a collection of information that is organized so that it can easily be accessed, managed, and updated.Databases are designed to offer an organized mechanism for storing, managing and retrieving information. They do so through the use of tables.It allows organizations to conveniently develop databases for various applications by database administrators (DBAs) and other specialists.The term "database" may be narrowed to specify particular aspects of organized collection of data and may refer to the logical database, to physical...

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