Clearing Corrupt Online Redo Log Files in Oracle 26ai

1. Diagnose the Failure Before Changing Redo

2. Inspect Group and Member Status

Use an authorized SQL*Plus administrative session at CDB$ROOT. Online redo belongs to the CDB; individual PDBs do not have independent online redo groups to clear. Confirm that the target is the intended primary database and that the session is permitted to perform the required administrative operation.

The database must be mounted or open for this procedure. If it is shut down, mount it using STARTUP MOUNT;. Do not repeat STARTUP on an already running instance or shut down an open database merely to match an example.

SHOW CON_NAME

SELECT name, database_role, open_mode, log_mode
FROM v$database;

SELECT group#, thread#, sequence#, status, archived, members
FROM v$log
ORDER BY thread#, group#;

SELECT group#, type, member, status
FROM v$logfile
ORDER BY group#, member;

V$LOG describes groups. V$LOGFILE lists their members, including the member path and recorded member status. A value such as STALE or INVALID in the latter view is not a group-recovery classification. Correlate it with the group state, error messages, and actual storage condition.

A null member status does not constitute a complete physical health check. Similarly, ARCHIVED = 'YES' records archiving status but does not prove that the archive remains accessible, readable, or backed up. Check the copies needed for recovery rather than relying solely on inventory metadata. The TYPE column also distinguishes online redo members from standby redo, which requires its own procedures.

Archiving does not make an ACTIVE group inactive. A log switch changes which group receives new redo, but the previous group can remain necessary for instance recovery. Checkpoint progress and archive completion answer different questions.

Decision Guide for an Inactive Group

Read the guide from the top: investigate the failure, restore temporary access where possible, and preserve any usable member. Only after those checks should the inactive-group branch be considered. The archive decision determines whether the unarchived contents would be discarded.

The image's “recovery impact assessed and accepted” decision is not an override of Oracle's restrictions. If an offline datafile depends on the log, leave the ordinary unarchived branch and address that dependency explicitly. Business acceptance of data loss cannot make a log eligible for clearing while Oracle still requires it for instance recovery.

3. Clear an Eligible Archived Group

Assume the investigation has established that all members of group 2 are damaged, the group is INACTIVE, its contents have been archived, and required archive copies remain usable. The storage destinations are available for reinitialization, and recovery dependencies have been checked. Group 2 is an example identifier; replace it with the group verified in your database.

SQL*Plus at CDB$ROOT, database mounted or open:

ALTER DATABASE CLEAR LOGFILE GROUP 2;

The command reinitializes the existing group for future use. It does not restore its previous sequence from the archive, perform datafile recovery, or start a new database incarnation. Do not append OPEN RESETLOGS to a routine clearing operation.

Oracle permits this eligible inactive-group procedure with the database mounted or open. That does not promise uninterrupted service: the underlying storage failure or the availability of other groups may already have affected the application. Check the command result and diagnostic messages before declaring the repair complete.

If the group is actually unarchived, stop and reassess. Do not automatically retry with UNARCHIVED just to make the statement succeed. The next branch changes the recoverability consequences.

4. Assess Unarchived Redo Before Discarding It

An inactive group may contain changes already written to the current datafiles while still being essential to recover an older backup. Clearing it without an archive can therefore leave today's database usable but break the path from yesterday's backup to today's state.

Before accepting that loss, investigate usable members, accessible storage copies, archive copies, and any applicable standby resources. Identify the thread and sequence that would be discarded and which retained backups or offline files require it. Where a usable copy can still be archived, preserve it using the appropriate procedure. Attempting to archive destroyed contents cannot reconstruct them.

For an eligible INACTIVE group whose unarchived contents will be discarded, after the recovery impact has been established and accepted and offline-file dependencies have been resolved, the alternative command is:

ALTER DATABASE CLEAR UNARCHIVED LOGFILE GROUP 2;

UNARCHIVED permits reuse without first archiving those contents. It does not waive the requirements associated with group state or offline-file recovery. Backups that require the discarded redo may no longer support complete recovery through that interval.

Do not describe this as instantly deleting every transaction from current datafiles. Nor does it automatically make every backup useless. The important question is whether a particular recovery path needs the missing redo. A backup may still support an earlier target or a different valid recovery path, depending on the available material.

Establish New Backup Coverage Immediately

Oracle's inactive-unarchived procedure calls for immediately backing up the database and its control file after clearing. Establish a new usable recovery starting point that does not depend on the discarded group. Include the redo needed to recover that new backup, and verify that the operation finishes successfully.

When the database is in a suitable state and RMAN backup destinations, channels, and required keys are available, an illustrative root-connected RMAN backup sequence is:

BACKUP DATABASE PLUS ARCHIVELOG;
BACKUP CURRENT CONTROLFILE;

This is post-clear backup work, not part of the SQL clearing syntax. Reconcile archive inventory and resolve missing-log or other backup errors through the backup procedure. Do not report protection as restored merely because the commands were submitted. A new backup cannot recreate the discarded sequence or repair an older recovery chain.

For an archived group whose required redo remains available, clearing does not inherently impose this same lost-history condition. Assess backup needs from the incident rather than claiming that every CLEAR operation has identical consequences.

5. Address Offline Datafile Dependencies

ALTER DATABASE CLEAR UNARCHIVED LOGFILE GROUP 2
  UNRECOVERABLE DATAFILE;

When the Group Is Active or Current

The inactive-group decision guide intentionally stops at ACTIVE or CURRENT. A noncurrent ACTIVE group in a database that is still running may become inactive after a successful checkpoint, as described in the Backup and Recovery User's Guide. Recheck the actual state afterward; merely requesting a checkpoint does not establish eligibility.

If the checkpoint cannot complete or the instance has stopped, assess the available recovery options. Depending on the surviving files and history, these may include restoring access, obtaining a usable redo copy, Flashback Database when its prerequisites hold, or restoring backups and performing incomplete recovery. Each option has its own endpoint and availability consequences.

The full CLEAR command has special thread and state cases beyond this lesson. Avoid the blanket claim that a CURRENT group can never be cleared under any circumstances. Equally, those special cases do not justify applying this single-instance inactive-group example to a failed current group.

RAC adds thread and instance coordination; Data Guard adds transport, apply, and standby recovery requirements. Verify those dependencies using the applicable administration procedure before changing primary redo. Mounting a database does not remove its recovery requirements.

Why Dropping and Recreating Is Not a Shortcut

A rejected CLEAR statement is a reason to understand the restriction. Dropping and recreating a group cannot restore its lost contents and is not a way to evade a recovery requirement. DROP has its own rules concerning archiving, group state, and the minimum number of groups in a thread.

Clearing can be useful where dropping would violate the minimum group count because it reinitializes the existing group. That difference does not eliminate the need to preserve required redo. Adding a new group provides future writing capacity, not a replacement for historical changes in the failed group.

If a usable member survives, use the relevant member-maintenance procedure and preserve that copy. Do not make an operating-system copy of an actively changing member and assume it is a consistent repair source. Member additions, removals, and storage relocation each require their own checks.

If Clearing Fails or Is Interrupted

CLEAR can fail while recreating a file on damaged storage. Oracle may already have recorded the attempted clearing in the control file before the physical write fails. A lingering clearing state therefore does not prove that the group has been successfully repaired.

Inspect the reported I/O error, every member destination, the alert log, and the relevant trace output. Correct the storage or naming problem and follow the documented interrupted-clear procedure. After an instance failure, that procedure may require reissuing the clear after restart; it is not a reason to repeatedly retry against an unresolved fault.

Do not delete all members or substitute another destructive command just to remove an error message. Record what the first attempt changed so subsequent recovery decisions reflect the current state.

Verify the Result and Recovery Coverage

After successful clearing, inspect the affected group and all its members from the same authorized root session:

SELECT group#, thread#, sequence#, status, archived, members
FROM v$log
WHERE group# = 2;

SELECT group#, type, member, status
FROM v$logfile
WHERE group# = 2
ORDER BY member;

A newly cleared group can be UNUSED until it is used. Do not force a log switch simply to make its status match an example. Instead, verify the operation's completion, storage accessibility, intended member redundancy, and absence of unresolved clearing errors.

Monitor subsequent normal redo use and archiving. For configurations with standby databases, also verify the relevant transport and apply requirements. Confirm completion of the new database and control-file backup when unarchived redo was discarded.

Document the failed paths, group, thread, sequence, action taken, and affected recovery coverage. Retain usable archives and backups according to the resulting recovery plan. Successful reinitialization restores a redo structure; verified backup and redo coverage establish what can be recovered after the next failure.

Technical basis: Oracle AI Database Backup and Recovery User's Guide, 26ai, G43741-04, May 2026, sections 37.7.1–37.7.2.2; the ALTER DATABASE reference; and the redo log administration guide.

The next lesson explains recovery involving inactive online redo logs.