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  Oracle Data File Management
  Add Date : 2018-11-21      
  1. Overview of data files

Oracle database data files (files with an extension of DBF) file is used to save the data in the database, system data, data dictionary, temporary data, index data, application data, etc. is physically stored in the data file. The user operates the data in the database, such as data insert, delete, modify and query, its essence is the data file operations. The size of all data files occupy space determines the size of the database capacity.

In the Oracle database, in order to improve the efficiency of the system, the user is not directly on the data file, the data from the database but the process will start with the user needs the data file is read into the data cache buffer cache, then the data from the cache District data back to the user, which can improve the reusability of the system, reduce disk I / O. If the user modifies the data in the data buffer cache, under certain conditions, by the DBWR process writes dirty data in the data file. This "memory external memory after the first" approach greatly improves the efficiency of the system.

In the Oracle database, although the data file attached table space exists, but you can separate the data file management, including modifying the measured data file is created, the size of the data files, data files offline and online operations, data file name and location change, delete data files and data file information inquiries.

Oracle database has a special data file called a temporary data file, a temporary database table space. Temporary data file content is temporary, under certain conditions, automatically released. Temporary files corresponding to other data files are called permanent data files.

In the Oracle database, the data file is attached to the table space exists. A table space can contain one or more data files, but a data file can only belong to a table space. Logically, the database consists of table space; physically, the database constituted by the data file.

2. Guidelines for the management of data files

 Guidelines for the management of data files include a reasonable amount to set the storage location of the data file, the data file size and data files of three aspects.

2.1 to determine the number of data files

2.2 determining the size of the data file

It should estimate the potential size of the space required for database objects when you create a table space to determine the size of data files. The database is running, you can add new data files or modify the size of data files to table space needed to expand the table space. When determining the size of the data file, in conjunction with its consideration of the remaining disk space usage.

2.3 Setting storage location of data files

Since the operation of the database eventually translate data file operations, so in the course of the operation of the database data files will be frequently read and write operations. In order to improve I / O efficiency, eliminate competition, it should be a reasonable allocation of the storage location of the data file.

1) will require concurrent access to data files on different drives to improve the efficiency of the system to read and write.

2) data files and control files. Redo log files are stored dispersed on different disks, can enhance the operating efficiency of the database, but also can reduce the extent of the damage database from media failure. In the database during operation, the system needs to operate in parallel data files, control files and redo log files, these files scattered in different physical disks can operate in parallel to improve system efficiency.

3. Create Data File

Since the Oracle database, the data file is attached to the table space exists, so the process of creating a data file is essentially the process of adding data files to table space. You can create a data file when you create a database, create a table space in the database operation and maintenance procedures may be added to the data file for the table space. It should be based on the size of the database table space objects to be stored, and the number of disk space, etc., to determine the number and size of the data file.

4. Modify the data file size

Automatic extension of data files 4.1

In the Oracle database, the database with the change in data capacity, you can adjust the size of data files. There is a change in the size of the data files two ways, one is automatically extended mode setting data file, the other is to reset the data file size.

4.2 to manually change the size of data files

In the Oracle database, you can manually modify the size of the data file after the data file is created. If the database storage space, you can increase the size of the data file to solve, without the need to create a new data file for the database, which is the number of data files has been reached for the database limit the number of cases is very effective. If the data file has a large amount of surplus space can be used to reduce the data storage method for recovering files, avoiding wasting storage space. Manually change the size of the data file extension method for large file table space more useful, because you can not add new data files to a large table space.

5. Change the name and location of the data file

After the data file is created, you can change their names and locations. Through case rename or move data files, you can not change the logical database storage structures, the physical storage structure of the database to adjust.

Operations change the data file name and location can be found in table space levels, may be performed at the database level. In the table space levels mean change operation data file name and location of the application affects only the current table space does not affect the application of other table spaces. At the database level in the database in a loading state is carried out, the database is not open at this time, all applications are stopped.

6 delete data files

You can use the following statement to delete the specified table space empty data file.

ALTER TABLESPACE ...... DROP DATAFILE: Remove permanent table space specified in the empty data file.

ALTER TABLESPACE ...... DROP TEMPFILE: Delete the temporary table space specified in the temporary data file empty.

The so-called empty empty temporary data files or data file is a file allocation for all zones have been recovered. Delete data files or colleagues temporary data files, control files and deletes the data dictionary information related to the data file, and the operating system will delete the corresponding physical file.

By following some constraints when deleting data files or temporary data files:

The database must be running in the open state.
Data file must be empty. If you want to delete a non-empty data file that can be used by removing the data file to your table space to achieve.
You can not delete the first table space or only one data file.
You can not be deleted from the dictionary migration management to the local management of the read-only table space data file.
You can not delete SYSTEM table space in the data file.
You can not delete locally managed tablespace offline data files.
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