Guidelines for Control Files - Oracle 10g

This section describes guidelines you can use to manage the control files for a database, and contains the following topics:

  • Provide Filenames for the Control Files
  • Multiplex Control Files on Different Disks
  • Back Up Control Files
  • Manage the Size of Control Files

Provide Filenames for the Control Files

You specify control file names using the CONTROL_FILES initialization parameter in the atabase initialization parameter. The instance recognizes and opens all the listed file during startup, and the instance writes to and maintains all listed control files during database operation.

If you do not specify files for CONTROL_FILES before database creation:

  • If you are not using Oracle-managed files, then the database creates a control file and uses a default filename. The default name is operating system specific.
  • If you are using Oracle-managed files, then the initialization parameters you set to enable that feature determine the name and location of the control files

Multiplex Control Files on Different Disks

Every Oracle Database should have at least two control files, each stored on a different physical disk. If a control file is damaged due to a disk failure, the associated instance must be shut down. Once the disk drive is repaired, the damaged control file can be restored using the intact copy of the control file from the other disk and the instance can be restarted. In this case, no media recovery is required.

The behavior of multiplexed control files is this:

  • The database writes to all filenames listed for the initialization parameter CONTROL _FILES in the database initialization parameter file.
  • The database reads only the first file listed in the CONTROL _FILES parameter during database operation.
  • If any of the control files become unavailable during database operation, the instance becomes inoperable and should be aborted.

One way to multiplex control files is to store a control file copy on every disk drive that stores members of redo log groups, if the redo log is multiplexed. By storing control files in these locations, you minimize the risk that all control files and all groups of the redo log will be lost in a single disk failure.

Back Up Control Files

It is very important that you back up your control files. This is true initially, and every time you change the physical structure of your database. Such structural changes include:

  • Adding, dropping, or renaming datafiles
  • Adding or dropping a tablespace, or altering the read/write state of the tablespace
  • Adding or dropping redo log files or groups

Manage the Size of Control Files

The main determinants of the size of a control file are the values set for the MAXDATAFILES, MAXLOGFILES, MAXLOGMEMBERS, MAXLOGHISTORY, and MAXINSTANCES parameters in the CREATE DATABASE statement that created the associated database. Increasing the values of these parameters increases the size of a control file of the associated database.

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