As DBA we are aware that Oracle is a mixture of CRD files. Now we are going to have look at Redolog.



Let’s have a technical definition of Redolog.

The most crucial structure for recovery operations is the redo log, which consists of two or more preallocated files that store all changes made to the database as they occur. Every instance of an Oracle Database has an associated redo log to protect the database in case of an instance failure.

Check Redo Log file Status: with the help of given select query.

The log files have the following status values:

  • USED         Indicates either that a log has just been added but never used.
  • CURRENT  Indicates a valid log that is in use.
  • ACTIVE      Indicates a valid log file that is not currently in use.
  • CLEARING Indicates a log is being re-created as an empty log due to DBA action.
  • CLEARING CURRENT Means that a current log is being cleared of a closed thread. If a log stays in this status, it could indicate there is some failure in the log switch.
  • INACTIVE  Means that the log is no longer needed for instance recovery but may be needed for media recovery.

The v$logfile table has a status indicator that gives these additional codes:

  • INVALID File is inaccessible.
  • STALE     File contents are incomplete (such as when an instance is shut down with SHUTDOWN ABORT or due to a system crash).
  • DELETED File is no longer used.
  • Null   File in use.

Adding Redo Log Groups:

Adding Redo Log Members:

Check the file Location of redo log files:

Dropping Online Redo Log Member:

Dropping Online Redo Log Groups:

Move Redo Log File Destinations

Forcing Log Switch:

Forcing Checkpoint:

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