Oracle Server Architecture
One of the first things that one needs to understand about the Oracle RDBMS (Relational Database Management System) is the difference between the terms: “database” and the “instance˳” This article will discuss the term “database˳” Briefly, the term database, refers only to the physical files on the operating system˳
The Oracle Database
An Oracle database (as opposed to an Oracle instance, which are processes in memory) is a group of files that reside on the physical hardware disk drives and actually store the data˳ These files consist of:
- Data Files: these files contain all the user and application data, as well as undo information, and meta data about the data file itself˳
- Control Files: these files are the brain of the database and contain information that define the meta data (i˳e˳ data about the data) including the names, locations, and types of the all the other database files˳
- Online Redo Log Files: these files contain database redo information, or the information to keep track of all changes made to the database if a database needs to be restored and recovered from a database backup˳ If the database is in “no archive log mode,” these online redo log files will be written over as they fill up and cycle to the next one˳
- Archive Log Files: if the database is in “archive log mode” these files contain the online redo log file information (see above) that have been archived before they are written over˳ Most databases are in “archive log mode” unless they contain data that will never need to be recovered in between a cold, offline backup˳ Only databases in “archive log mode” can be backed up with a hot, or online backup˳
- Temp Files: these files contain temporary data segments that are generated when database sorts are performed˳
Database Files Examples:
In a SAP Oracle database environment, the below are typical examples of the directory, or file system structure, and file names˳ These are examples only˳ Your system directory structure and file naming standards may vary˳
Data Files:
/oracle/CPQ/sapdata1/system_1/system˳data1
/oracle/CPQ/sapdata2/temp_1/temp˳data1cd
/oracle/CPQ/sapdata3/undo_1/undo˳data1
/oracle/CPQ/sapdata4/sr3db_1/sr3db˳data1
Control Files:
/oracle/CPQ/sapdata1/cntrl/cntrlCPQ˳dbf
/oracle/CPQ/origlogA/cntrl/cntrlCPQ˳dbf
Online Redo Log Files:
/oracle/CPQ/origlogA/log_g1m1˳dbf
/oracle/CPQ/origlogB/log_g2m1˳dbf
/oracle/CPQ/mirrlogA/log_g1m2˳dbf
/oracle/CPQ/mirrlogB/log_g2m2˳dbf
Archive Log Files:
/oracle/CPQ/oraarch/CPQarch1_3325_769904912˳dbf
/oracle/CPQ/oraarch/CPQarch1_3326_769904912˳dbf
/oracle/CPQ/oraarch/CPQarch1_3327_769904912˳dbf
Temp Files:
/oracle/CPQ/sapdata2/temp_1/temp˳data1
Congratulations! You have now learned one part of the Oracle Server Architecture: what is meant by the term “database˳” This short treatment is not meant to cover the topic in detail, but is meant as an introduction, and an enjoyable, painless way toward mastering a complex topic˳ You should next learn about the Oracle Instance˳
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