Concept of Control File The control file is a small binary file for recording the physical structure of the database. A control file is only a database. Create a control file when you create a database. When the physical structure of the database changes, Oracle will update the control file. Users cannot edit the control file, and the modification of the control file is complete by Oracle.
The startup and normal operation of the database are inseparable from the control file. When you start the database, Oracle gets the name and location of the control file from the initialization parameter file, open the control file, and then read the information of the data file and the online log file from the control file, and finally open the database. When the database is running, Oracle modifies the control file, so once the control file is corrupted, the database will not function properly.
Database information is as follows
Database Name (Database Name
Creating a Database's Timestamp
Data File Name and Location
Name and location of online log file
table space information
log history (log history)
archive log information
Current log sequence number (Log Sequence Number)
The size of the control file is below Several parameters decided:
MaxInstances< p> when add, rename, delete a data file or an online log file, Oracle server process (server process) will be updated to reflect this change the control file database structure immediately. So, Oracle always warns us that after the structure of the database changes, back up the control file. The log write process LGWR is responsible for recording the current log sequence number into the control file. The checkpoint process CKPT is responsible for recording the information of the checkpoint to the control file. The archive process is responsible for recording the information of the archive log into the control file.
value of the recording position control file CONTROL_FILES the initialization parameters. Typically, DBA should mirror control files, distribute each control file to different physical disks, when a disaster occurs, even if one of the control files are corrupted, the data will not be lost, and the entire database will not cause the entire database to be paralyzed.