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. It includes the redo entries and the unique log sequence number of the identical member of the redo log group. For example, if you are multiplexing your redo log, and if group 1 contains identical member files a_log1 and b_log1, then the archiver process (ARCn) will archive one of these member files. Should a_log1 become corrupted, then ARCn can still archive the identical b_log1. The archived redo log contains a copy of every group created since you enabled archiving.

When the database is running in ARCHIVELOG mode, the log writer process (LGWR) cannot reuse and hence overwrite a redo log group until it has been archived. The background process ARCn automates archiving operations when automatic archiving is enabled. The database starts multiple archiver processes as needed to ensure that the archiving of filled redo logs does not fall behind.

You can use archived redo logs to:

Recover a database

Update a standby database

Get information about the history of a database using the LogMiner utility


Related Post: NOARCHIVELOG and ARCHIVELOG Mode

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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 are mechanisms to access the physical data block defined on disk, Oracle must also have a logical structure that will relate down to that data block as your tables are created within the data files and as they grow over time. This is done by three logical structures that are kept for every object created in Oracle. These three structures are data blocks, extents, and segments.


Related Video:- Oracle DBA - Logical Database Structure

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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 not rename the tables stored in it. An Oracle database is a set of files that store Oracle data in persistent disk storage.The physical structure of an Oracle database includes only three types of files: control files, data files, and redo log files

Data files

A data file is a physical file on disk that was created by Oracle Database and contains data structures such as tables and indexes. A temp file is a data file that belongs to a temporary tablespace. The data is written to these files in an Oracle proprietary format that cannot be read by other programs.

Control files

A control file is a root file that tracks the physical components of the database.

Online redo log files

The online redo log is a set of files containing records of changes made to data.

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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 the relationship between the physical and logical structures of a database.

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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 has a logical and a physical structure. The physical structure of the database is the set of operating system files in the database. An Oracle database consists of three file types.

• Data files containing the actual data in the database
• Redo logs containing a record of changes made to the database to enable recovery of     the data in case of failures
• Control files containing information necessary to maintain and verify database integrity Other Key File Structures

     The Oracle server also uses other files that are not part of the database:  

• The parameter file defines the characteristics of an Oracle instance. For example, it contains parameters that size some of the memory structures in the SGA.
• The password file authenticates users privileged to start up and shut down an Oracle instance.
• Archived redo log files are offline copies of the redo log files that may be necessary to recover from media failures.

Related video:- Introduction to Oracle Database Administration - Oracle DBA

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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 when one required to a particular data. The individual has to go through considerable amount of sheets in order to one data. Lots of places were also required to keep them in files. Moreover, the entire process was time consuming and quite boring also. For the particular work quite a number of persons were needed to be appointed.

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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, maintenance and repair of an organization's database. They are also known by the titles Database Coordinator or Database Programmer, and is closely related to the Database Analyst, Database Modeller, Programmer Analyst, and Systems Manager. The role includes the development and design of database strategies, monitoring and improving database performance and capacity, and planning for future expansion requirements. They may also plan, co-ordinate and implement security measures to safeguard the database.

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