Why multiplex redo log group ?

Hello,
Why should we multiplex redo log groups if we have only file system which is already mirrored. Is there any one who had an incident when he has only one redo log member per group placed on a mirrored file system but still got corrupted and he felt better to have multiple members even if they reside on the same file system (which is mirrored)
Thanks
Salman

Ansiktet wrote:
EdStevens wrote:
Salman Qureshi wrote:
Hello,
Why should we multiplex redo log groups if we have only file system which is already mirrored. Is there any one who had an incident when he has only one redo log member per group placed on a mirrored file system but still got corrupted and he felt better to have multiple members even if they reside on the same file system (which is mirrored)
Thanks
SalmanThe mirror won't protect you from an SA who deletes '/u01/oradata/redo01.log' because he is running out of space on /u01 and figures its safe to delete a log file.
Or similar types of errors.
The redo and control files are simply too critical to put all your eggs in one basket when planning their protection.:) Thats why you should not use Oracle default .log on redo, instead .dbf or .dbl can be used. THat's why I use the older (pre-10g) default of .rdo for redo logs
However, has this happend anyone for real, that a SA delete Oracle files? Where do you think I came up with the example?
HOw about an SA (or maybe the kind of "fresher" we often see here, Taking a look at a "log" file with notepad?
If he is isnt stupid he should know that Oracle resides on /u01 partion (for example), and should not delete files there without consulting the DBA."should" is the operative word there. There is no accounting for corporate cultures and attitudes.
But end the end, my example was to illustrate that not all problems with redo and control files are mitigated with disk mirroring.

Similar Messages

Multiplexing redo log files

I am using 9i R2 database.
I just want to clear some doubts.
I am having 3 redo log groups with one member each.
Now for mutiplexing redo log files
i want to add one one member to each group so
that each group will have 2 members in some different path.
my current path of log member are
/oracle/files/a1.log (group 1)
/oracle/files/b1.log (group 2)
/oracle/files/c1.log (group 3)
I want to add
/oracle/sysfiles/a2.log (group 1)
/oracle/sysfiles/b2.log (group 2)
/oracle/sysfiles/c2.log (group 3)
A--So is there any need to take database in any mode (nomunt,mount) or i can do it while
database is open ?
I will issue
ALTER DATABASE ADD LOGFILE MEMBER /oracle/sysfiles/a2.log TO GROUP 1 ;
First in inactive group,then
alter system switch logfile; (To make 2 group inactive....and then 3)
B-- All memebers in a redolog group must be of same size? if i am having
100 M.B. of one member(a1.log) is there no need to specify size while adding new member(a2.log)?
Can some one validate and correct my steps or suggest me regarding this?

Hi,
All the solutions are in oracle documentaiton.
See, Members of the same multiplexed redo log group must be the same size (that all member in with in the group ) and Members of different groups can have different sizes. If the same of Files are different resultant would be the with Checkpoints. Since you can not gurantee that Checkpoints will occur at regular internals (Log switch with respect log members). Better to follow the Rules of traffic similarly follow the instrcutions of ORACLE Documentation.. :-)
- Pavan Kumar N

Standby redo log group for particular thread

hi masters,
actually i am performing an experiment to create physical standbyt database on the same machine as my primary database.
i ma going according to 'data guard admin guide'. while section for ading standby redo log group,it says that you have to add standby redo log group to "thread"....
what is this thread? and how can i foind to which thread i have to assign the next redo log group??
how can i find current thread??
what if i dont add "to thread' clause in my statement:-
ALTER DATABASE ADD STANDBY LOGFILE THREAD 5
2> ('/oracle/dbs/log1c.rdo','/oracle/dbs/log2c.rdo') SIZE 500M;
thanks and regards
VD

Vikrant,
First a question: Do you have a RAC instance? If so the paragraph even doesn't apply to you and I'm not sure why you are questioning it.
Secondly
"The THREAD clause is required only if you want to add one or more standby redo log
file groups to a specific primary database thread. If you do not include the THREAD
clause and the configuration uses Real Application Clusters (RAC), Data Guard will
automatically assign standby redo log file groups to threads at runtime as they are
needed by the various RAC instances."
this means you dont have to specify thread for RAC,as it will allocate one according to current thread.
Your conclusion is incorrect.
Where do you read the word 'current'?
Oracle will likely simply make sure each instance has sufficient standby redolog groups, the requirement is 1 standby redolog group per group + 1 extra.
Sybrand Bakker
Senior Oracle DBA

Redo Logs Groups and Members

Hi -
I have a few questions regarding redo log groups and naming conventions I was hoping someone could address or point me to some docs.
I am multiplexing my control file and redo logs across HDDs for an XE installation.
The original logs created at install have the naming form of:
O1_MF_1_462H1GK7_.LOG.
1. What is behind the naming scheme (specifically the _462H1GK7_ section)?
2. Is there a generally recognized naming scheme for adding new group members in XE?
3. I noticed that with any XE install I have done, the redo logs groups default to Group 1 and Group 3, with no Group 2 to be found. Is this normal/required? If not, is it best to add group 2 and then remove group 3? I'm not sure if has much bearing here, but the 10gR2 docs state that skipping group numbers will consume space in the control files.
Thanks in advance for any assistance,
Scott

The odd-looking filename is from using Oracle Managed Files (OMF). You can override the naming scheme or create your own groups and members. Very common to include "redo" in the file name along with group and member identifiers. An example would be:
<path>/redo01a.log
<path>/redo01b.log
<path>/redo02a.log
etc.
You can see group 01 has two members, a and b. Can also include the SID in the file name as well, but that can be identified via the path. 462H1GK7 is a unique identifier generated by Oracle. It has no meaning.
I don't know about XE not creating a group 2. Were there group 2 file(s) left over from a previous install (although the OMF probably would have ignored the existing files)? If creating the files manually, you can use "reuse" to use existing files.

Multiplexing Redo Log and maximum protection mode.

Assume that during writing into redo logs the instance crashes. As a result, members of active redo group are not synchronized, some of them had more data. How Oracle will handle this when instance starts? And there can be case when at startup time some members that had more redo before crash, are lost.
Now assume that we have standby database with maximum protection mode. After LGWR has written to local redo logs and before writing to standby redo logs, primary instance crashes. In this case standby site lost last transaction.
Is it correct? Thanks.

Assume that during writing into redo logs the instance crashes. As a result, members of active redo group are not synchronized, some of them had more data. How Oracle will handle this when instance starts? And there can be case when at startup time some members that had more redo before crash, are lost.
Members of a particular group are written concurrently by LGWR, all members of a log group will have same data. If any member of a particular group is lost or not reachable, oracle will read from the available log member during instance recovery.
Multiplexing Redo Log Files
http://docs.oracle.com/cd/B19306_01/server.102/b14231/onlineredo.htm#i1006249
To answer your second question,In this mode no transaction commits on primary unless the redo is also written on atleast one standby database, otherwise primary will go down.
Check below
Maximum Protection
http://docs.oracle.com/cd/B28359_01/server.111/b28294/protection.htm#CHDHFHJI

Online Redo Log groups

Dear All,
How to check the health of redo log file, we have 200 MB undo tablespace in our production server is it enough for huge transactions. Can I check how much time my redo log file data have been overwritten?
Further in which situation we will add Online Redo Log Groups and which situation we will add Log Members.
My rollback segment is using System tablespace is it recommended?
What is recommendation about 1 redo log group is redo log member or 1 redo log group is multiple redo log members.

Thanks Mr. Nicolas. for your informative guidence.
Can I check how much time my redo log file data have been overwritten?Check v$loghist.
We have 218 records in v$loghist, it means 218 times data have been overwritten, i think its not good. Can you guide me how to rectyify this.
in which situation we will add Online Redo Log GroupsIn case of checkpoint not complete reported into alert.log.
How to findout checkpoint entry in alert.log
which situation we will add Log Members.This is the redolog multiplexing, at least two members for each redolog group.
Ok, Can we do multiplexing for members or just do for groups.
My rollback segment is using System tablespace is it recommended?No.
OK, can we change rollback segments tablespace.
1 redo log group is redo log member or 1 redo log group is multiple redo log membersA minimum of two redolog group with two members for each.
After, it depend of your db activity.
We have just one member for each group and we have three groups, so whats ur recommnedation we will add 1 member in each group.

Unable to drop a Redo Log Group

Hi,
My database is running on version 11.1.0.7 on OEL platform.
I am trying to delete one of the Active Redo Log Group, it fails with the below error. Could someone please help me fix this issue?
SQL > select * from v$log;
    GROUP#    THREAD# SEQUENCE#      BYTES    MEMBERS ARCHIVED STATUS                                           FIRST_CHANGE# FIRST_TIME
        10          1       8017 524288000          2 YES       INACTIVE                                            1.2120E+13 17-JUN-2012 19:43:49
        11          1       8018 524288000          2 YES       INACTIVE                                            1.2120E+13 18-JUN-2012 06:49:45
        12          1       8019 524288000          2 YES       INACTIVE                                            1.2120E+13 18-JUN-2012 16:56:43
        13          1       8021 524288000          2 YES       INACTIVE                                            1.2120E+13 18-JUN-2012 23:18:07
        14          1       8020 524288000          2 YES       INACTIVE                                            1.2120E+13 18-JUN-2012 23:14:27
        15          1       8022 524288000          2 NO        CURRENT                                             1.2120E+13 19-JUN-2012 01:07:27
        16          2       6835 524288000          2 YES       INACTIVE                                            1.2120E+13 18-JUN-2012 23:15:46
        17          2       6836 524288000          2 YES       INACTIVE                                            1.2120E+13 18-JUN-2012 23:18:04
        18          2       6837 524288000          2 YES       INACTIVE                                            1.2120E+13 18-JUN-2012 23:20:22
        19          2       6838 524288000          2 YES       INACTIVE                                            1.2120E+13 18-JUN-2012 23:22:38
        20          2       6839 524288000          2 NO        CURRENT                                             1.2120E+13 19-JUN-2012 01:07:24
        21          2       6832 524288000          2 YES       INACTIVE                                            1.2120E+13 18-JUN-2012 23:11:45
        22          3       3771 524288000          2 YES       INACTIVE                                            1.2103E+13 09-SEP-2011 22:04:11
        23          3       3772 524288000          2 YES       INACTIVE                                            1.2103E+13 09-SEP-2011 23:55:55
        24          3       3773 524288000          2 YES       ACTIVE                                              1.2103E+13 09-SEP-2011 23:55:59
        25          3       3766 524288000          2 YES       INACTIVE                                            1.2103E+13 08-SEP-2011 22:05:29
        26          3       3767 524288000          2 YES       INACTIVE                                            1.2103E+13 08-SEP-2011 22:05:50
        27          3       3768 524288000          2 YES       INACTIVE                                            1.2103E+13 09-SEP-2011 14:02:05
SQL > archive log list;
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            /archive/MYCSMA/MYCSMA2
Oldest online log sequence     6832
Next log sequence to archive   6839
Current log sequence           6839
SQL > archive log all;
ORA-00271: there are no logs that need archiving
SQL > ALTER SYSTEM ARCHIVE LOG GROUP 24;
ALTER SYSTEM ARCHIVE LOG GROUP 24
ERROR at line 1:
ORA-16013: log 24 sequence# 3773 does not need archiving
SQL > alter database drop LOGFILE group 24;
alter database drop LOGFILE group 24
ERROR at line 1:
ORA-01623: log 24 is current log for instance MYCSMA3 (thread 3) - cannot drop
ORA-00312: online log 24 thread 3: '/u247/oradata/MYCSMA/redo24_1.log'
ORA-00312: online log 24 thread 3: '/u247/oradata/MYCSMA/redo24_2.log'This was previously a 3 node RAC and when it was moved to a different machine, it got build with a 2-node RAC.
Hence thread 3 is no more required. Thats why I am planning to drop these Redo Log Groups.
Thanks!

Hi;
All information cover at:
NOTE:102995.1 - Maintenance of Online Redo Log Groups and Members
Regard
Helios

Confused about standby redo log groups

hi masters,
i am little bit confuse about creating redo log group for standby database,as per document number of standby redo group depends on following equation.
(maximum number of logfiles for each thread + 1) * maximum number of threads
but i dont know where to fing threads? actually i would like to know about thread in deep.
how to find current thread?
thanks and regards
VD

is it really possible that we can install standby and primary on same host??
yes its possible and i have done it many times within the same machine.
For yours confusion about spfile ,i agree document recommend you to use spfile which is for DG broker handling if you go with DG borker in future only.
There is no concern spfile using is an integral step for primary and standby database implementation you can go with pfile but good is use spfile.Anyhow you always keep pfile on that basis you created spfile,i said you make an entry within pfile then mount yours standby database with this pfile or you can create spfile from this pfile after adding these parameter within pfile,i said cause you might be adding this parmeter from SQL prompt.
1. logs are not getting transfered(even i configure listener using net manager)
2.logs are not getting archived at standby diectory.
3.'ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT FROM SESSION' NEVER COMPLETE ITS RECOVERY
4. when tried to open database it always note it 'always' said system datafile is not from sufficiently old backup.
5.i tried 'alter database recover managed standby database camncel' also.Read yours alert log file and paste the latest log here..
Khurram

After increasing redo log groups we are getting given alerts continvously

earlier having 6 redo log groups with 32 MB.but 7 days back our database was hangs .no one was able to login into sqlplus except sys user ,but not able to perform any dml operation.after rebooting our 2-node RAC instances it was running fine nearly about 6-7 hrs and again hangs.we did 4-5 times and same thing happend again and again.so we had added more redo logs of 100 MB size and removed previous one.then our hangs problem resolved but continvously getting given things in alert logs for both RAC instances(9.2.0.8).our os is linux
{color:#ff0000}Wed Dec 3 05:04:31 2008
ARC1: Completed archiving log 15 thread 1 sequence 282036
ARC1: Evaluating archive log 17 thread 1 sequence 282037
ARC1: Unable to archive log 17 thread 1 sequence 282037
Log actively being archived by another process
ARC1: Evaluating archive log 13 thread 1 sequence 282038
ARC1: Beginning to archive log 13 thread 1 sequence 282038
Creating archive destination LOG_ARCHIVE_DEST_2: 'SBMEMS'
Creating archive destination LOG_ARCHIVE_DEST_1: '/MemsArchive/0001_0000282038.arc'
Wed Dec 3 05:04:31 2008
Thread 1 advanced to log sequence 282040
Current log# 15 seq# 282040 mem# 0: /MemsRedoA/redo15_1.log
Current log# 15 seq# 282040 mem# 1: /MemsRedoB/redo15_2.log
Wed Dec 3 05:05:21 2008
ARC1: Completed archiving log 13 thread 1 sequence 282038
ARC1: Evaluating archive log 17 thread 1 sequence 282037
{color}{color:#ff0000}*ARC1: Unable to archive log 17 thread 1 sequence 282037*
Log actively being archived by another process
ARC1: Evaluating archive log 18 thread 1 sequence 282039
ARC1: Beginning to archive log 18 thread 1 sequence 282039
Creating archive destination LOG_ARCHIVE_DEST_2: 'SBMEMS'
Creating archive destination LOG_ARCHIVE_DEST_1: '/MemsArchive/0001_0000282039.arc'
Wed Dec 3 05:05:21 2008
ARC0: Completed archiving log 17 thread 1 sequence 282037
ARC0: Evaluating archive log 18 thread 1 sequence 282039
ARC0: Unable to archive log 18 thread 1 sequence 282039
Log actively being archived by another process
ARC0: Evaluating archive log 18 thread 1 sequence 282039
{color}{color:#ff0000}*ARC0: Unable to archive log 18 thread 1 sequence 282039*
Log actively being archived by another process
ARC0: Evaluating archive log 18 thread 1 sequence 282039
{color}{color:#ff0000}*ARC0: Unable to archive log 18 thread 1 sequence 282039*
Log actively being archived by another process
ARC0: Evaluating archive log 18 thread 1 sequence 282039
ARC0: Unable to archive log 18 thread 1 sequence 282039
Log actively being archived by another process
ARC0: Evaluating archive log 18 thread 1 sequence 282039
ARC0: Unable to archive log 18 thread 1 sequence 282039
Log actively being archived by another process
ARC0: Evaluating archive log 18 thread 1 sequence 282039
ARC0: Unable to archive log 18 thread 1 sequence 282039
Log actively being archived by another process
Wed Dec 3 05:05:49 2008
ARC1: Completed archiving log 18 thread 1 sequence 282039
Wed Dec 3 09:01:02 2008
Thread 1 advanced to log sequence 282041
Current log# 17 seq# 282041 mem# 0: /MemsRedoA/redo17_1.log
Current log# 17 seq# 282041 mem# 1: /MemsRedoB/redo17_2.log
Wed Dec 3 09:01:02 2008
ARC1: Evaluating archive log 15 thread 1 sequence 282040
ARC1: Beginning to archive log 15 thread 1 sequence 282040
Creating archive destination LOG_ARCHIVE_DEST_2: 'SBMEMS'
Creating archive destination LOG_ARCHIVE_DEST_1: '/MemsArchive/0001_0000282040.arc'
Wed Dec 3 09:01:29 2008
ARC0: Evaluating archive log 15 thread 1 sequence 282040
{color}{color:#ff0000}*ARC0: Unable to archive log 15 thread 1 sequence 282040*
Log actively being archived by another process
Wed Dec 3 09:01:37 2008
ARC1: Completed archiving log 15 thread 1 sequence 282040
{color}ORADB1:MEMS1:oracle$
please suggest solution for this.
Thanks

As Sybrand pointed out, this msg can be ignored. It clearly states that a given arch process cannot archive a given redo because that redo is already being handled by a different arch process. If you follow your alert log a little further, you'll see that the referenced thread is eventually completed.
I'd be curious to see the alert log from when you were locked up and only sysdba could log on. See what led you to believe that adding more redo log groups would solve your problem.

Online redo log group needed??

hey guys!
Am about to recreate the clone file of the clone db, open it using recover it until cancel using backup controlfile and apply all necessary archive logs!
My question is, does ai need to have online redo log group of the production db? since ai have all the archive log, so ai think while recraeting the control file, online redo log group will be created too?
Thanks!

while recraeting the control file, online redo log group will be created tooWhile creating control file, online redo log group doesn't get created. After applying all the archivel logs you have to open the database with RESET LOG option and then oracle will create redo logs for you.
Best of Luck !!
Daljit Singh

Redo Log Groups

Call me stupid, but for some reason I've decided to get certified as a DBA even though I have always been a developer. Honestly, its not my fault. The choices in the development track are pretty boring...
Anyway, while pouring through the Backup/Recovery documentation, I run across this:
Every database must have at least two online redo log groups.
Each redo log group contains at least one online redo log member,
which is a physical file containing the redo records.I decided to check and see if I have "at least two online redo log groups" for my play database. Now, I am very very confused.
I think this query shows my 3 log members, but for some reason the 1st column makes me think I have 3 log groups:
select group#, member from v$logfile
    GROUP# MEMBER
         3 /var/opt/oracle/oradata/db92/redo03.log
         2 /var/opt/oracle/oradata/db92/redo02.log
         1 /var/opt/oracle/oradata/db92/redo01.logI only know of one place where my online redo is located:
ls $ORACLE_BASE/oradata/db92
redo01.log redo02.log redo03.logCan someone help me figure out if I have one-group and three-members??
Any comments are welcome,
Stan

This information can help you:
Adding Redo Log File Groups: Examples
The following statement adds a redo log file group with two members and identifies it with a GROUP parameter value of 3:
ALTER DATABASE
ADD LOGFILE GROUP 3
('diska:log3.log' ,
'diskb:log3.log') SIZE 50K;
The following statement adds a redo log file group containing two members to thread 5 (in a Real Application Clusters environment) and assigns it a GROUP parameter value of 4:
ALTER DATABASE
ADD LOGFILE THREAD 5 GROUP 4
('diska:log4.log',
'diskb:log4:log');
Dropping Log File Members: Example
The following statement drops one redo log file member added in the previous example:
ALTER DATABASE
DROP LOGFILE MEMBER 'diskb:log3.log';
The following statement drops all members of the redo log file group 3:
ALTER DATABASE DROP LOGFILE GROUP 3;
Adding Redo Log File Group Members: Example
The following statement adds a member to the redo log file group added in the previous example:
ALTER DATABASE
ADD LOGFILE MEMBER 'diskc:log3.log'
TO GROUP 3;
Renaming a Log File Member: Example
The following statement renames a redo log file member:
ALTER DATABASE
RENAME FILE 'diskc:log3.log' TO 'diskb:log3.log';
The preceding statement only changes the member of the redo log group from one file to another. The statement does not actually change the name of the file 'diskc:log3.log' to 'diskb:log3.log'. You must perform this operation through your operating system.
Joel P�rez

All redo log groups is active

Hello dear gurus!
After shutting database with option "abort"
we have unconsisten state of datafiles.
I ask to explain :
1) - does the ARCH background processes flash whole redo buffer into redolog ?
(In other words how reached consistency if all redo log groups was in active state before shutting down ?)
2) Where buffer contents in this case are dumped ?
Thanks and best regards,
Pavel
Edited by: Pavel on Jul 19, 2012 9:49 PM

Pavel wrote:
Hello dear gurus!
After shutting database with option "abort"
we have unconsisten state of datafiles.That's expected as checkpoint didn't happen. Issue a startup and instance recovery should take care of everything.
I ask to explain :
1) - does the ARCH background processes flash whole redo buffer into redolog ?ARCH process or LGWR? How does this relates to your current question?
(In other words how reached consistency if all redo log groups was in active state before shutting down ?)As I said, issue a startup of the instance and it should take care of the things.
2) Where buffer contents in this case are dumped ?Which case? Your questions are a bit fuzzy you see. Let's stick to one question at one time and follow it shall we?
Aman....

Log_file_name_convert , db_recovery_area and multiplexed redo logs

Hi, I have a confusion here, need help.
I have multiplexed redo log members on both asm diskgroup DATA, FRA.
My log_file_name_convert='+DATA', '+DATA'
and db_recovery_area ='+FRA'
db_create_online_log_dest_1=+DAT
Are above parameters right?

log_file_name_convert is simply a string replacing function.Its same behaviour like DB_FILE_NAME_CONVERT
So all entries of <first> will be replaced by <second> and the <third> entry will be replaced by the <fourth> and so on.Yes the strings should be in even numbers like 2,4,6,8.. ther should be sequence for the source & destination diskgroup and so on.
So if you would have:
'DATA','REPLACE','FRA','REPFRA'
all occurences of DATA will be replaced with RAPLACE. But this would also mean ORADATAGRAM would be replaced to ORAREPLACEGRAM.If any ORL's / SRL's are created in DATA in source, by mentioning LOG_FILE_NAME_CONVERT those will be created to the connected proceeding string...
Can you point out please where is mistake in my previous post?

Delete all redo log groups

Friends,
Suddenly I have to delete all of my redo log groups (REDO01.LOG,REDO02.LOG,REDO03.LOG) from my database . Now I cannot open my database . I am using Oracle 10g database . I have no cold backup of my database but have a RMAN backup . Now How can I restore my redo log groups .
Can anybody plz help me .. ...

if you are working in archive mode
SQL> startup
ORACLE instance started.
Total System Global Area 272629760 bytes
Fixed Size 1290136 bytes
Variable Size 213909608 bytes
Database Buffers 50331648 bytes
Redo Buffers 7098368 bytes
Database mounted.
ORA-00313: open failed for members of log group 1 of thread 1
ORA-00312: online log 1 thread 1:
'D:\ORACLE\PRODUCT\10.2.0\ORADATA\PEEGT\REDO01.LOG'
SQL> recover database until cancel;
Media recovery complete.
SQL> alter database open resetlogs;
Database altered.
Backup your database...

Abot loss online Redo log group

Hi,
Is there different from recovering between loss CURRENT online redo log group and ACTIVE online redo log group?
Both of them are needed to incomplete recovery, right?

For CURRENT redolog recovery:
startup mount
recover database until cancel;
alter database open resetlogs;
For ACTIVE redolog recovery:
If the database is still running, force a checkpoint by issuing the following command:
alter system checkpoint;
If above was successful and if the lost group has been archived then issue:
alter database clear logfile group <number of the online redo log group>;
And if the lost group has NOT been archived then issue:
alter database clear logfile unarchived group <number of the online redo log group>;
alter database open;
If the database is not running (crashed) then
startup mount
recover database until cancel;
alter database open resetlogs;
Daljit Singh

Why multiplex redo log group ?

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