Oracle Redo Logs

Oracle Redo Log Files Version 11.2.0.3

General Information

Data Dictionary Objects

ALL_LOG_GROUPS	V$LOG	V$INSTANCE_LOG_GROUP
DBA_LOG_GROUPS	V$LOGFILE	V$LOG_HISTORY
LOG$	V$LOGHIST	V$THREAD
USER_LOG_GROUPS

init File Parameters

log_checkpoint_timeout ... set to 0

Log Files With Redundancy
(Group with multiple members)

LOGFILE
GROUP 1 ('/u01/oradata/redo1a.log','/u05/oradata/redo1b.log') SIZE 2G,
GROUP 2 ('/u02/oradata/redo2a.log','/u06/oradata/redo2b.log') SIZE 2G,
GROUP 3 ('/u03/oradata/redo3a.log','/u07/oradata/redo3b.log') SIZE 2G,
GROUP 4 ('/u04/oradata/redo4a.log','/u08/oradata/redo4b.log') SIZE 2G

Log Files Without Redundancy

LOGFILE
GROUP 1 '/u01/oradata/redo01.log'SIZE 2G,
GROUP 2 '/u02/oradata/redo02.log'SIZE 2G,
GROUP 3 '/u03/oradata/redo03.log'SIZE 2G,
GROUP 4 '/u04/oradata/redo04.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 for 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
('/oracle/dbs/log1c.rdo', '/oracle/dbs/log2c.rdo') SIZE 500M;

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 4 ('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 4;

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>;

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 2;

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('01/01/2007','MM/DD/YYYY'))*86400 ssec
FROM dual;

ALTER SYSTEM DUMP LOGFILE 'c:\oracle\product\oradata\orabase\redo01.log' TIME MIN 579354757;

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 * FROM (
SELECT * FROM (
    SELECT TO_CHAR(FIRST_TIME, 'DD/MM') AS "DAY"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '00', 1, 0)), '99') "00"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '01', 1, 0)), '99') "01"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '02', 1, 0)), '99') "02"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '03', 1, 0)), '99') "03"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '04', 1, 0)), '99') "04"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '05', 1, 0)), '99') "05"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '06', 1, 0)), '99') "06"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '07', 1, 0)), '99') "07"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '08', 1, 0)), '99') "08"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '09', 1, 0)), '99') "09"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '10', 1, 0)), '99') "10"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '11', 1, 0)), '99') "11"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '12', 1, 0)), '99') "12"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '13', 1, 0)), '99') "13"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '14', 1, 0)), '99') "14"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '15', 1, 0)), '99') "15"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '16', 1, 0)), '99') "16"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '17', 1, 0)), '99') "17"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '18', 1, 0)), '99') "18"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '19', 1, 0)), '99') "19"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '20', 1, 0)), '99') "20"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '21', 1, 0)), '99') "21"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '22', 1, 0)), '99') "22"
    , TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '23', 1, 0)), '99') "23"
    FROM V$LOG_HISTORY
    WHERE extract(year FROM FIRST_TIME) = extract(year FROM sysdate)
    GROUP BY TO_CHAR(FIRST_TIME, 'DD/MM'))
ORDER BY TO_DATE(extract(year FROM sysdate) || DAY, 'YYYY DD/MM') DESC)
WHERE ROWNUM < 8
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;