Oracle physical and logical structures-(data files and tablespaces)

DBMS (DataBaseManagementSystem) database management system, as the name implies, is a data management system, so first you have to have data, then the management is through the Instance

DBMS (Data Base Management System) database Management System, as the name suggests, is a Data Management System, so first we have to have Data, and then the Management is through the Instance

DBMS (Data Base Management System) database Management System, as its name implies, is a Data Management System. Data must first be available and then managed through instances, an instance is a memory structure and background process. In short, it is a running program, and processes are generated when the program runs on the operating system. the data is actually a file in the operating system, and there is no big difference between the txt and word files that we are exposed to in peacetime. when there was no database, the data was saved in a file like txt, And Then edited directly or through some applications. however, common files have data redundancy, inconsistency, and security issues.

The most important content in relational databases is tables, which are stored in data files. the suffix of this file is dbf. you can use select * from dba_data_files; to view their locations. for example, in windows, c: \ app \ Administrator \ oradata \ ora11r2. on linux:/home/Oracle/oradata/ora11r2. however, we generally use a logical structure like tablespace to indirectly use data files.

The relationship between a tablespace and a data file is: a tablespace contains at least one data file, or multiple. A data file can only belong to one tablespace. this is equivalent to having many files under a folder on windows.

Relationship between tables and data files: Generally, a table belongs to a data file, however, when the table is large or the space of data files is quickly used up, a table may be stored in several data files. however, a table is only in one tablespace and does not belong to several tablespaces.

When you create a user, you can specify a tablespace. The table created by the user is saved to that tablespace by default. However, you can also specify to specify a tablespace when creating the table. multiple users can share one tablespace. after Oracle is installed, some data files and tablespaces are created by default.

The data file for the system tablespace is system. dbf: it is a bit like a windows C drive. Oracle system tables and data dictionaries are stored here. note that all user-created functions, stored procedures, and other objects are stored in the system tablespace (you can view this information through select * from dba_source ), only the table created by the user is saved to the tablespace specified by the user.

In the undo tablespace, Oracle will copy the old values to the tablespace before performing the DML operation. This is where the old values are deleted after the commit operation. The temp tablespace is sorted.

The preceding section describes the default tablespace created by the system. You can also create a tablespace by yourself: create tablespace mySpace datafile 'd: \ mydata '100 MB; -- We can add other parameters for more settings.

For more information about Oracle, see the Oracle topic page? Tid = 12

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