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This article introduces the relevant knowledge of "what are the physical files of Database". In the operation of actual cases, many people will encounter such a dilemma. Then let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Control file (Control File)

1. At least one control file is required for a database

2, the control file (binary file) is a very small (usually the smallest in the database) file, the size is generally about 1-5m.

3. During the operation of the database, whenever a database checkpoint occurs or the structure of the database is modified, oracle will modify the contents of the control file.

4. DBA can modify part of the contents of the control file through the OEM tool, but DBA and users should not modify the contents of the control file artificially, which is easy to destroy the control file.

Data file (Data File)

1. The data file is the operating system file that actually stores the actual data inserted into the database.

2. The data is written to the data file in an oracle-specific format, and other programs cannot read the data in the database file.

3. The size of the data files is directly related to the size of the database they store.

4. After the database writes the data, it will increase due to the automatic allocation of the new added area, but deleting the data will not reduce it, but will only make it have more free areas.

5. Except for SYSTEM tablespaces, any tablespace can be switched from online to offline.

6. When the tablespace goes offline, the data files that make up the tablespace go offline.

7. A data file in the tablespace can be set offline for database backup or recovery, otherwise it cannot be backed up.

8. Data is stored in user-defined tables, but data files also contain data dictionaries, modified data before image formation, indexes, and other types of structures.

Log file (Redo Log File)

1. When users modify the database, they actually modify the data in memory first, and then write the modified results in memory to the above data file in batches after a period of time. Oracle takes this approach mainly for performance reasons, because for data operations, memory is faster than hard drives.

2. Oracle uses the "online redo log file" to keep the modification results at any time, that is, oracle saves the modification results in memory to the "redo log file" at any time. "at any time" means that the modification results may have been written to the "redo log file" several times before writing the modification results to the data file. As a result, a failure causes the database to crash, and oracle can also use the information in the redo log file to recover the lost data. As long as the redo information for an operation is not lost, the redo information can be used to reproduce the operation.

3. Oracle uses redo log files in a circular manner, so each database needs at least 2 redo log files.

Parameter file

The configuration file records some important parameters when the Oracle database is running, such as the size of the data block, the configuration of the memory structure, and so on. The name is usually in init*.ora format, such as initCIMS.ora.

Archived document

Archive redo log files: offline copies of redo log files that may be necessary to recover from media failures.

Password file

Authenticate which users have the right to start and shut down Oracle instances.

Alarm log file

Some operations used to record data to help locate the point of failure

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