What data is saved in the data file

The data file stores the "data stored in the database". A data file is only associated with one database, and the data file of a database contains all database data; once created, the data file cannot change in size; a table space (logical unit of database storage) consists of one or more data files.

The operating environment of this tutorial: Windows 10 system, Dell G3 computer.

Data files (generally refers to database files) such as: each ORACLE database has one or more physical data files (data files). Data of logical database structures (such as tables, indexes) are physically stored in the database's data files.

A database has at least one primary data file and can have multiple secondary data files to store data that does not fit in the primary data file.

Features

A data file is only associated with one database, and the data file of a database contains all database data. Once created, data files cannot change size. A tablespace (a logical unit of database storage) consists of one or more data files. The data in the data file can be read and stored in the ORACLE internal storage area when needed. For example: the user wants to access some data in a table of the database. If the requested information is not in the memory storage area of ​​the database, it will be read from the corresponding data file and stored in the memory. When modifying and inserting new data, it is not necessary to write to the data file immediately. In order to reduce the total amount of disk output and improve performance, the data is stored in memory, and then the ORACLE background process DBWR determines how to write it to the corresponding data file.

Main Data File

The main data file consists of the initial data files in the main file group. A filegroup is a named collection of data files. Contains all database system tables, as well as objects and data not assigned to custom file groups. The main data file is the starting point of the database and points to other files in the database. Each database has a main data file and a main file group. The extension of the main data file is .mdf

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