Oracle - SPLessons

Chapter 9

Oracle Physical Storage Structures

Oracle Physical Storage Structures

The Oracle Physical Storage Structures is controlled by the operating  frame work documents that gives the conceptual physical stockpiling to the database.

One representative of an RDBMS is the autonomy of coherent information designs like views, index and tables from natural repository designs. Since natural and sensible designs are independent, to control natural storage of information beyond influencing access to coherent designs. For instance, In Oracle Physical Storage Structures changing the name of the database documents doesn’t change the tables name. An Oracle database is a collection of records that keep Oracle information in industrious circle stockpiling.

Physical Storage Structure

In Oracle Physical Storage Structures, Based on the classification of files the Oracle database can be classified into the following types.

Control files

Each database contain a control document or file. A control document contains sections that determine the natural design of the database. For instance, it holds the accompanying data.

  • Database term
  • term and region of data files and redo log files
  • Time stamp about formation of database.

It will convolute the oversight records, i.e., at the same point of time it preserves a number of indistinguishable control of duplicate records, to ensure against a decline including the control file.

Each moment when an  occurrence of an Oracle database begins, its control records distinguishes the database and retry log documents that should be opened for database operation to continue. In the event that the physical cosmetics of the database is adjusted and control document is consequently altered by Oracle to reverse the alteration. A control record is additionally utilized as a part of database recuperation.

The below example describes the concept of control files:

CREATE CONTROLFILE
   SET DATABASE prod
   LOGFILE GROUP 1 ('/u01/oracle/prod/redo01_01.log', 
                    '/u01/oracle/prod/redo01_02.log'),
           GROUP 2 ('/u01/oracle/prod/redo02_01.log', 
                    '/u01/oracle/prod/redo02_02.log'),
           GROUP 3 ('/u01/oracle/prod/redo03_01.log', 
                    '/u01/oracle/prod/redo03_02.log') 
   RESETLOGS
   DATAFILE '/u01/oracle/prod/system01.dbf' SIZE 3M,
            '/u01/oracle/prod/rbs01.dbs' SIZE 5M,
            '/u01/oracle/prod/users01.dbs' SIZE 5M,
            '/u01/oracle/prod/temp01.dbs' SIZE 5M
   MAXLOGFILES 50
   MAXLOGMEMBERS 3
   MAXLOGHISTORY 400
   MAXDATAFILES 200
   MAXINSTANCES 6
   ARCHIVELOG;

Data file structure

It contain one or more physical information files. The information files subsist all the database information’s. The information of legitimate database design are indexes and tables, is naturally put away in the data files dispensed for a database. The qualities of data files are:

  • A dataset can be connected to a single database.
  • Data files contain qualities collections for consequently extend when the database come up short of space.
  • One or more data files structure a coherent unit of database stockpiling called a table space.

Information in a dataset is perceived, as required, amid typical database application and put away in the collection store of Oracle. For instance, accept that a client needs to get to some information in a table of a database. In the way that the data is not same as the way that the data contained in the database, then it is used from the suitable data files and put away in consciousness.

Altered information is doesn’t necessary to keep inside the data record. To decrease the measure of plate access and to expand execution, information is pooled in memory and kept in touch with the proper data set at the same time, as dictated by the database author in process foundation process.

Redo log files

Each Oracle database has an arrangement contains more redo log records. The arrangement of redo log documents is altogether called as the re-try log for the database. A redo log is comprised of re-try sections.

The essential capacity of the re-try log is to report all progressions done to the information’s. If a break down restrict, alter information from being permanently recorded in the respective data files, then the progressions can be obtained from the redo log, so work is no way vanished from the database.

To secure against a disappointment including the redo log itself, Oracle permits a multiplexed redo log so that two or more duplicates of the re-try log can be kept up on various plates. The data in a redo log file record is utilized just to recuperate from the frame work or media failure that keeps database information from being composed to the data files. For instance, if an unexpected potential capacity black out ends database operation,then information in memory can’t be composed to the data files, and the information is incur. However, incur information can be recouped when the database is open, after potential capacity is renewed. By applying the data in the most recent redo log files records to the database data files, Oracle restores the database to the time at which the power failure happened.

The procedure of applying the redo log amid a recuperation or recovery operation is called rolling forward.

Summary

  • Oracle Physical storage structure – Data stored in the database will be saved in disc folder made up of frame work system  blocks.
  • Control files –  It contain the physical structure of database that records the  small files.
  • Data files – Data file is a part of oracle database and is used to store data.
  • Redo log files – A collection of file that reports all the alteration done in the database.