Oracle Redo Log Files
Version 12.1.0

General Information
Data Dictionary Objects
ALL_LOG_GROUPS USER_LOG_GROUPS V$INSTANCE_LOG_GROUP
CDB_LOG_GROUPS V$LOG V$LOG_HISTORY
DBA_LOG_GROUPS V$LOGFILE V$THREAD
LOG$ V$LOGHIST  
init File Parameters log_checkpoint_timeout ... set to 0
Log Files With Redundancy

(Group with multiple members)
LOGFILE
 GROUP 1 ('/u01/app/oracle/oradata/orabase/redo1a.log','/u05/app/oracle/fast_recoery_area/orabase/onelinelog/redo1b.log') SIZE 2G,
 GROUP 2 ('/u01/app/oracle/oradata/orabase/redo2a.log','/u05/app/oracle/fast_recoery_area/orabase/onelinelog/redo2b.log') SIZE 2G,
 GROUP 3 ('/u01/app/oracle/oradata/orabase/redo3a.log','/u05/app/oracle/fast_recoery_area/orabase/onelinelog/redo3b.log') SIZE 2G,
 GROUP 4 ('/u01/app/oracle/oradata/orabase/redo4a.log','/u05/app/oracle/fast_recoery_area/orabase/onelinelog/redo4b.log') SIZE 2G,
Log File Sizing As a rule-of-thumb one should try to balance archive logging between the following mutually exclusive criteria
  • The larger the log files the less frequent the log switches and the better performance
  • The smaller the log files the less risk of data loss in the event of log file corruption or a need to recover
The generally accepted balance point, in most organizations is archive log file switches once every 5 to 15 minutes: In other words 4 to 12 switches per hour.

Other advantages to consider in using the log file switch frequency recommended here, as opposed to fewer switches, are:
  • Fewer archivelog records and files to track
  • Fewer backup records for RMAN and backup software to track and maintain
  • Many backup appliances requires 1 file per set, so the more data that can backup at once the smaller the channel allocation overhead incurred and the faster backups and restores will take place
Status Privileges
Status Description
active The online redo log is active and required for instance recovery, but is not the log to which the database is currently writing. It may be in use for block recovery, and may or may not be archived.
clearing The log is being re-created as an empty log after an ALTER DATABASE CLEAR LOGFILE statement. After the log is cleared, then the status changes to UNUSED.
clearing_current The current log is being cleared of a closed thread. The log can stay in this status if there is some failure in the switch such as an I/O error writing the new log header.
current The online redo log is active, that is, needed for instance recovery, and it is the log to which the database is currently writing. The redo log can be open or closed.
inactive The log is no longer needed for instance recovery. It may be in use for media recovery, and may or may not be archived.
unused The online redo log has never been written to.
Related System Privileges
ALTER DATABASE ALTER SYSTEM  
 
Managing Log File Groups
Add a redo log file group ALTER DATABASE ADD LOGFILE
('<log_member_path_and_name>', '<log_member_path_and_name>')
SIZE <integer> <K | M | G>;
ALTER DATABASE ADD LOGFILE
('/u01/app/oracle/oradata/orabase/redo4a.log','/u05/app/oracle/fast_recoery_area/orabase/onelinelog/redo4b.log') SIZE 2G;
Add a redo log file group and specifying the group number ALTER DATABASE ADD LOGFILE GROUP <group_number>
('<log_member_path_and_name>') SIZE <integer> <K | M | G>;
ALTER DATABASE ADD LOGFILE GROUP 5 ('c:\temp\newlog1.log') SIZE 500M;
Relocate redo log files ALTER DATABASE RENAME FILE '<existing_path_and_file_name>'
TO '<new_path_and_file_name>';
conn / as sysdba

SELECT member
FROM v_$logfile;

SHUTDOWN;

host

$ cp /u03/logs/log1a.log /u04/logs/log1a.log
$ cp /u03/logs/log1b.log /u05/logs/log1b.log

$ exit

startup mount

ALTER DATABASE RENAME FILE '/u03/logs/log1a.log' TO '/u04/oradata/log1a.log';

ALTER DATABASE RENAME FILE '/u04/logs/log1b.log' TO '/u05/oradata/log1b.log';

ALTER DATABASE OPEN;

host

$ rm /u03/logs/log1a.log
$ rm /u03/logs/log1b.log

$ exit

SELECT member
FROM v_$logfile;
Drop a redo log file group ALTER DATABASE DROP LOGFILE GROUP <group_number>;
ALTER DATABASE DROP LOGFILE GROUP 5;
 
Manage Log File Members
Adding a single log file group member ALTER DATABASE ADD LOGFILE MEMBER '<log_member_path_and_name>' TO GROUP <group_number>;
ALTER DATABASE ADD LOGFILE MEMBER '/oracle/dbs/log2b.log' TO GROUP 2;
Add a log group containing two members ALTER DATABASE ADD LOGFILE GROUP <integer>
(<logfile_path_and_name>, <logfile_path_and_name>)
SIZE <integer><K | M  | G>;
ALTER DATABASE ADD LOGFILE GROUP 4 ('/u01/logs/redo4a.log', '/u02/logs/redo4b.log') SIZE 500M;
Drop Log File Group ALTER DATABASE DROP [STANDBY] LOGFILE GROUP <integer>;
SELECT group#, status
FROM gv$log;

ALTER DATABASE DROP LOGFILE GROUP 5;
Dropping log file group member ALTER DATABASE DROP [STANDBY] LOGFILE MEMBER <logfile_member_path_and_name>;
SELECT *
FROM gv$logfile
WHERE group# IN (
  SELECT group#
  FROM gv$log
  WHERE status = 'INACTIVE');

ALTER DATABASE DROP LOGFILE MEMBER '/oracle/dbs/log3c.log';
Drop Log File by Descriptor ALTER DATABASE DROP [STANDBY] LOGFILE <file_name>;
ALTER DATABASE DROP LOGFILE '/oracle/dbs/log3c.log';
 
Manage Log File Threads
Add a redo log containing two members to a thread ALTER DATABASE ADD LOGFILE THREAD <integer> GROUP <integer>
(<logfile_path_and_name>, <logfile_path_and_name>);
ALTER DATABASE ADD LOGFILE THREAD 5 GROUP 3
('/u03/oradabase/redo315.log', '/home/oracle/orabase/redo325.log');
 
Dumping Log Files
Dumping a log file to trace ALTER SYSTEM DUMP LOGFILE '<logfile_path_and_name>'
DBA MIN <file_number> <block_number>
DBA MAX <file_number> <block_number>;

or

ALTER SYSTEM DUMP LOGFILE '<logfile_path_and_name>'
TIME MIN <value>
TIME MIN <value>;
conn uwclass/uwclass

alter session set nls_date_format='MM/DD/YYYY HH24:MI:SS';

SELECT SYSDATE
FROM dual;

CREATE TABLE test AS
SELECT owner, object_name, object_type
FROM all_objects;

INSERT INTO test
(owner, object_name, object_type)
VALUES
('UWCLASS', 'log_dump', 'TEST');

COMMIT;

conn / as sysdba

SELECT ((SYSDATE-1/1440)-TO_DATE('01/01/2013','MM/DD/YYYY'))*86400 ssec
FROM dual;

ALTER SYSTEM DUMP LOGFILE 'c:\oracle\product\oradata\orabase\redo01.log' TIME MIN 4997217;
 
Related Queries
This query can be used to create a report giving a graphical view of dates and times of log file usage set linesize 121
col 00 format 99
col 01 format 99
col 02 format 99
col 03 format 99
col 04 format 99
col 05 format 99
col 06 format 99
col 07 format 99
col 08 format 99
col 09 format 99
col 10 format 99
col 11 format 99
col 12 format 99
col 13 format 99
col 14 format 99
col 15 format 99
col 16 format 99
col 17 format 99
col 18 format 99
col 19 format 99
col 20 format 99
col 21 format 99
col 22 format 99
col 23 format 99

SELECT TO_CHAR(first_time,'MMDD') MMDD,
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'00',1,0)),'99') "00",
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'01',1,0)),'99') "01",
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'02',1,0)),'99') "02",
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'03',1,0)),'99') "03",
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'04',1,0)),'99') "04",
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'05',1,0)),'99') "05",
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'06',1,0)),'99') "06",
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'07',1,0)),'99') "07",
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'08',1,0)),'99') "08",
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'09',1,0)),'99') "09",
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'10',1,0)),'99') "10",
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'11',1,0)),'99') "11",
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'12',1,0)),'99') "12",
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'13',1,0)),'99') "13",
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'14',1,0)),'99') "14",
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'15',1,0)),'99') "15",
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'16',1,0)),'99') "16",
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'17',1,0)),'99') "17",
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'18',1,0)),'99') "18",
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'19',1,0)),'99') "19",
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'20',1,0)),'99') "20",
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'21',1,0)),'99') "21",
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'22',1,0)),'99') "22",
TO_CHAR(SUM(DECODE(TO_CHAR(first_time,'HH24'),'23',1,0)),'99') "23"
FROM v$log_history
GROUP BY TO_CHAR(first_time,'MMDD')
ORDER BY 1;
Redo Log generation rate query from Jonathan Lewis [Click Here] SELECT TO_CHAR(first_time,'dd hh24:mi:ss') first_time,
ROUND(24 * 60 * (LEAD(first_time,1) OVER (ORDER BY first_time) - first_time),2) minutes
FROM v$log_history v
ORDER BY recid;
View information on log files SELECT *
FROM gv$log;
View information on log file history SELECT thread#, first_change#,
TO_CHAR(first_time,'MM-DD-YY HH12:MIPM'), next_change#
FROM gv$log_history;
Forcing log file switches ALTER SYSTEM SWITCH LOGFILE;

or

ALTER SYSTEM CHECKPOINT;
Clear a log file if it has become corrupt ALTER DATABASE CLEAR LOGFILE GROUP <group_number>;

-- this statement overcomes two situations where dropping redo logs is not possible: If there are only two log groups The corrupt redo log file belongs to the current group.
ALTER DATABASE CLEAR LOGFILE GROUP 4;
Clear A Log File If It Has Become Corrupt And Avoid Archiving ALTER DATABASE CLEAR UNARCHIVED LOGFILE GROUP <group_number>;

-- use this version of clearing a log file if the corrupt log file has not been archived.
ALTER DATABASE CLEAR UNARCHIVED LOGFILE GROUP 3;

Related Topics
Archive Log Mode
Backup & Restore
Control Files
DBMS_LOGMNR
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