Redo log members in a group

Hi,
I am running 10gRac on Linux
I have 4 groups with 1 member each (50MB).
The DB is running in noarchive mode
I heard there is recommendation to have at least 2 members in each group.
Now how can I check if I should add more members to the groups?
Thanks

Hi br00klynZ00,
just imagine that you loose the only member of an unarchive group.
Maybe teh CURRENT?!
What do you do then?
You habe lost data then if you have a crash in addition because you cannot recover your lost instance.
So you should definitely have at least two members for each group!
=;-)
Hope this clarifies a little what the problem is.
BR,
Lutz

Similar Messages

Best way to move redo log from one disk group to another in ASM?

Hi All,
Our db is 10.2.0.3 RAC db. And database servers are window 2003 server.
We need to move more than 50 redo logs (some are regular and some are standby) which are not redundant from one disk group to another. Say we need to move from disk group 1 to 2. Here are the options we are thinking about but not sure which one is the best from easiness and safety prospective.
Thank you very much for your help in advance.
Shirley
Option 1:
1)     shutdown immediate
2)     copy log files from disk group 1 to disk group2 using RMAN (need to research on this)
3)     startup mount
4)     alter database rename file ….
5)     Open database open
6)     delete the redo files from disk group 1 in ASM (how?)
Option 2:
1)     create a set of redo log groups in disk group 2
2)     drop the redo log groups in disk group 1 when they are inactive and have been archived
3)     delete the redo files associated with those dropped groups from disk group 1 (how?) (According to Oracle menu: when you drop the redo log group the operating system files are not deleted and you need to manually delete those files)
Option 3:
1)     create a set of redo members in disk group 2 for each redo log group in disk group 1
2)     drop the redo log memebers in disk group 1
3)     delete the redo files from disk group 1 associated with the dropped members

Absolutely not, they are not even remotely similar concepts.
OMF: Oracle Managed Files. It is an RDMBS feature, no matter what your storage technology is, Oracle will take care of file naming and location, you only have to define the size of a file, and in the case of a tablespace on an OMF DB Configuration you only need to issue a command similar to this:
CREATE TABLESPACE <TSName>; So the OMF environment creates an autoextensible datafile at the predefined location with 100M by default as its initial size.
On ASM it should only be required to specify '+DGroupName' as the datafile or redo log file argument so it can be fully managed by ASM.
EMC. http://www.emc.com No further commens on it.
~ Madrid
http://hrivera99.blogspot.com

Writing in redo log members

Hi i have a couple of questions
1) what is the max value i can set for MAXLOGFILES in controlfile? that is maximum how many redo log groups i can have in a database(when not considering space occupied by log members)
2) I had a 2 log groups with 2 members in each. how LGWR writes into log members of each group. whether it will done in serial(sequential order) or parallel? If it is sequential, when LGWR writes into 2nd member of one group if i perform a log switch, will it wait till it completes writing into that member and switches to another group?
thanks in advance

>>> I had a 2 log groups with 2 members in each. how LGWR writes into log members of each group. whether it will done in serial(sequential order) or parallel? If it is sequential, when LGWR writes into 2nd member of one group if i perform a log switch, will it wait till it completes writing into that member and switches to another group?
Mr.Howard Rodger wrote:-
There is only ever one Log Writer process. Unlike Database Writer, for example, which can have several 'clone' processes sharing the work burden, redo log records must be written to disk sequentially -and that means only one process can be in charge of working out what to write to disk. If that wasn't true, you might come to grief when a series of transactions have dependencies. If you first create a new product record and then raise a new sale record to indicate that the new product has just been sold, for example, you need the product transaction to be recorded before the sale transaction -otherwise, during a recovery, you might end up trying to sell a product that doesn't exist yet. To prevent that logical nonsense from happening, therefore, a single Log Writer process writes everything in the correct sequence.
I hope it helps
Regards
Nisanth V Santhan

Redo log add and new group

Hi,
I have problem with one of the redo log file i issued the ALTER DATABASE CLEAR LOGFILE GROUP 3; command. the status right now is clearing since last some hours.
Can i create new redo log and assign to group 3. will the status will be inactive or active? how to add redo log and group please explain!
Thanks

user12020966 wrote:
Hi,
I have problem with one of the redo log file i issued the ALTER DATABASE CLEAR LOGFILE GROUP 3; command. the status right now is clearing since last some hours.
Can i create new redo log and assign to group 3. will the status will be inactive or active? how to add redo log and group please explain!
Thanksafer you create redo log group it wil be inactive because nothing has been written to it after you apply alter system switch file the new group will start to write the redo record and it status will be active but if the circule in group 3

Filling of redo log members

Hello!
Could you please explain , is the filling of redo log members async or sync?
Thanks and regards,
Pavel

Pavel wrote:
Hello!
Could you please explain , is the filling of redo log members async or sync?
Yes, the filling of redo log members is async or sync.
For example, on exadata, redo can be written to both SSD and hard disk, and whichever is done first is sync, and the other isn't.
On DG, you can do it either way.
If you look at the various internal mechanisms for private redo strands, you can have several situations.
[url http://asktom.oracle.com/pls/apex/f?p=100:11:0::::P11_QUESTION_ID:60447282988010]You can also have async commits, as [url http://asktom.oracle.com/pls/asktom/f?p=100:11:::::P11_QUESTION_ID:1415454871121#20061201507022]PL/SQL has done since forever.
See also http://www.pythian.com/news/1098/tuning-log-file-sync-event-waits/

Redo Log Members & RAID 5

Hi,
My production database servers run on HP-XP storage, raid 5. Currently the redo logs are striped on 16 disks, as raw files. I use 5 groups, 2 members in each group.
I wanted to hear your opinion, if two members are still necessary with todays storage hardware, considering the mirroring already done in the hardware level.
What is the benefit today for having more than one member in a group, and do you think it's worth the IO price most of us are still paying...
Thanks in advance,
Idan.

For example here:
http://asktom.oracle.com/pls/ask/f?p=4950:8:::::F4950_P8_DISPLAYID:359617936136
Try search google btw. There are plenty of articles.
Just if you read concepts of RAID you will learn that RAID 5 is not good for write intensive operations (redo logs are write intensive).

Configure archiver to read from both redo log members

Hi, We have moved our Data Warehouse to a new SAN. The luns for the redo logs are getting hit heavily. Just trying to find out if on AIX it is possible to configure archiver so that it reads from both members, current iostat data shows reads of the redo logs are only happening against the first member of each group and none against the second member. Thanks Tom Cullen

See a recent discussion on this issue :
Redo log Doubt
Hemant K Chitale

Dropping Redo Log Members

hi
in Oracle documentation they said you can't drop a member if it's an active
but i tried it in Oracle's Database 10g and it's dropped successfully
what happend ?
The link is :
http://download.oracle.com/docs/cd/B28359_01/server.111/b28310/onlineredo005.htm
Thanks

>
but i tried it in Oracle's Database 10g and it's dropped successfully >
You would have done alter system switch logfile before dropping the active redo logsfile.
Refer to the link for the status of the redo logs [http://download.oracle.com/docs/cd/B14117_01/server.101/b10755/dynviews_1126.htm#REFRN30127]
23:36:05 venture >select * from v$log;
    GROUP#    THREAD# SEQUENCE#      BYTES    MEMBERS ARC STATUS           FIRST_CHANGE# FIRST_TIM
         1          1         29 104857600          1 NO INACTIVE               7457724 07-DEC-08
         2          1         30 104857600          1 NO INACTIVE               7794484 08-DEC-08
         3          1         33 104857600          1 NO CURRENT                8016830 09-DEC-08
         4          1         31 104857600          1 NO INACTIVE               8016825 09-DEC-08
         5          1         32 104857600          1 NO INACTIVE               8016827 09-DEC-08
23:38:01 venture >create table test as select rownum id,'TEST' name from dual connect by level <= 10000000;
Table created.
Elapsed: 00:00:20.09
23:39:27 venture >select * from v$log;
    GROUP#    THREAD# SEQUENCE#      BYTES    MEMBERS ARC STATUS           FIRST_CHANGE# FIRST_TIM
         1          1         29 104857600          1 NO INACTIVE               7457724 07-DEC-08
         2          1         30 104857600          1 NO INACTIVE               7794484 08-DEC-08
         3          1         33 104857600          1 NO CURRENT                8016830 09-DEC-08
         4          1         31 104857600          1 NO INACTIVE               8016825 09-DEC-08
         5          1         32 104857600          1 NO INACTIVE               8016827 09-DEC-08
Elapsed: 00:00:00.00
23:39:34 venture >alter database drop logfile group 3;
alter database drop logfile group 3
ERROR at line 1:
ORA-01623: log 3 is current log for thread 1 - cannot drop
ORA-00312: online log 3 thread 1: 'D:\ORACLE\ORADATA\VENTURE\REDO03.LOG'
Elapsed: 00:00:00.01
23:39:51 venture >alter system switch logfile;
System altered.
Elapsed: 00:00:00.01
23:40:02 venture >select * from v$log;
    GROUP#    THREAD# SEQUENCE#      BYTES    MEMBERS ARC STATUS           FIRST_CHANGE# FIRST_TIM
         1          1         34 104857600          1 NO CURRENT                8017910 09-DEC-08
         2          1         30 104857600          1 NO INACTIVE               7794484 08-DEC-08
         3          1         33 104857600          1 NO ACTIVE                 8016830 09-DEC-08
         4          1         31 104857600          1 NO INACTIVE               8016825 09-DEC-08
         5          1         32 104857600          1 NO INACTIVE               8016827 09-DEC-08
Elapsed: 00:00:00.00
23:40:03 venture >alter database drop logfile group 3;
alter database drop logfile group 3
ERROR at line 1:
ORA-01624: log 3 needed for crash recovery of thread 1
ORA-00312: online log 3 thread 1: 'D:\ORACLE\ORADATA\VENTURE\REDO03.LOG'
Elapsed: 00:00:00.00
23:40:11 venture >alter system switch logfile;
System altered.
Elapsed: 00:00:00.01
23:40:25 venture >select * from v$log;
    GROUP#    THREAD# SEQUENCE#      BYTES    MEMBERS ARC STATUS           FIRST_CHANGE# FIRST_TIM
         1          1         34 104857600          1 NO INACTIVE               8017910 09-DEC-08
         2          1         35 104857600          1 NO CURRENT                8018022 09-DEC-08
         3          1         33 104857600          1 NO INACTIVE               8016830 09-DEC-08
         4          1         31 104857600          1 NO INACTIVE               8016825 09-DEC-08
         5          1         32 104857600          1 NO INACTIVE               8016827 09-DEC-08
Elapsed: 00:00:00.00
23:40:28 venture >alter database drop logfile group 3;
Database altered.
Elapsed: 00:00:00.00
23:40:42 venture >select * from v$log;
    GROUP#    THREAD# SEQUENCE#      BYTES    MEMBERS ARC STATUS           FIRST_CHANGE# FIRST_TIM
         1          1         34 104857600          1 NO INACTIVE               8017910 09-DEC-08
         2          1         35 104857600          1 NO CURRENT                8018022 09-DEC-08
         4          1         31 104857600          1 NO INACTIVE               8016825 09-DEC-08
         5          1         32 104857600          1 NO INACTIVE               8016827 09-DEC-08
Elapsed: 00:00:00.00
23:40:46 venture >HTH
Anand

REDO Log Members

Hello-
I was looking at some old database installs and if the REDO logs are stored in the same file directory then isn't having two members
not very useful and only good for placing these on another file system ?
Thanks-

Admin. Guide says http://download.oracle.com/docs/cd/E11882_01/server.112/e17120/onlineredo002.htm#ADMIN11309
>
To protect against a failure involving the redo log itself, Oracle Database allows a multiplexed redo log, meaning that two or more identical copies of the redo log can be automatically maintained in separate locations. For the most benefit, these locations should be on separate disks. Even if all copies of the redo log are on the same disk, however, the redundancy can help protect against I/O errors, file corruption, and so on.

Larger redo log file members or more log groups

Oracle 11gR1 RHEL5 64 bit
Hi,
I was wondering what is better from a perfomance tuning perspective. I have log swiches occuring every 2 minutes in our production database. I know definitely that our log file members are too small (100MB). The redo log sizing tool in OEM told me to make it 40G according to the fast_start_mttr_target setting which is set to 600. Now, my question is what is better to do?
1. Increase the size of my current redo log members? Right now there are 4 groups with 2 members in each.
OR
2. Should I create additonal redo log groups (4 more) and then re-rerun the sizing tool or query the v$instance_recovery view?
Which is better? tradeoffs?
Thanks all.

If you want to reduce the number (frequency) of Log Switches, you should increase the size of the Online Redo Logs -- ie create new Log File Groups of a larger size and drop the older ones.
If the issue is "checkpoint not complete" waits, then either
a. Increasing the size of the Log Files
or
b. Increasing the number of Log Files
is doable
Note that if you increase the number but not the size, you still have a checkpoint every N Mbytes -- ie, possibly too frequently !
On the other hand if you increase your size to be very large, at every switch, the Archiver is going to kick in with a large Read + large Write operation -- reading that Redo Log of N GBytes and writing it out to the archive log target location, imposing that additional I/O spike on your system. (Writing to filesystem will go through the FileSystem Buffers so if your database SGA isn't very large and your database performance relies on hitting the FileSystem Buffer Cache to avoid Disk Reads, that performance will be impacted as a large portion of the FileSystem Buffer Cache will be taken over by the Archiver for some time).
Hemant K Chitale
http://hemantoracledba.blogspot.com

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.

Log members per log group

Apologies in advance if this has been answered already, I did try to find the answer first.
Is a log group in a data warehouse meant to have more than one member per group? That is, if there are three log groups, is there meant to be three (or, for example six) log members?
Also, what does it mean if one of the log members are not the same size as the others (as reported in a Toad health check)?

A Redo Log group consists of redo logfiles called members that saves the identical information. These redo log members can only belong ot single redo log group.
Is a log group in a data warehouse meant to have more than one member per group?Good idea is to have 3 redolog groups with two members each.
Cheers, Bhupinder

What will heppen if redo logs at os level get deleted

Friends,
need 1 answer about the query: what will heppen if redo logs at os level get deleted.

how can i find where are my multiplexed redo logs, so that i can copy it from there
SQL> shutdown abort
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.
Total System Global Area 534462464 bytes
Fixed Size                  2256912 bytes
Variable Size             398462960 bytes
Database Buffers          125829120 bytes
Redo Buffers                7913472 bytes
Database mounted.
SQL> select * from v$logfile
2 ;
    GROUP# STATUS TYPE
MEMBER
IS_
         3         ONLINE
C:\O\ORADATA\XE\REDO03.LOG
NO
         2         ONLINE
C:\O\ORADATA\XE\REDO02.LOG
NO
    GROUP# STATUS TYPE
MEMBER
IS_
         1         ONLINE
C:\O\ORADATA\XE\REDO01.LOG
NO                                         However, Oracle knows about the multiplexing, so if your logs were multiplexed properly (using redo log members), Oracle would already have known about them and identified that there was one available.
Just goes to show you (if this is, in fact what you did), don't just go blindly deleting files that have a ".LOG" extension.

Redo log files deleted

Hello,
One of my friend deleted redo log and control files of one machine in cluster environment. Oracle parallel server(8.1.7) is installed on this cluster.
Redo log and control files of the second disk is still there.
Can i copy the control files and redo log files of the second disk to the first one...??? Will it work ???
Please let me know how should I go by it...??
Thanking in anticipation.
Regards,
Rajeev

Hello,
I don't have any experiences with cluster/parallel server. But in general:
1. Controlfile: shutdown database and cp exisiting controlfile to "old" destination. Filename must be similar to deleted controlfile.
2. Redo Logs: Drop and recreate groups step by step (no user activity recommended). Database won't crash, because members are still "alive" on second disk.
HTH,
juergen_klinsmann

How does LGWR write redo log files, I am puzzled!

The document says:
The LGWR concurrently writes the same information to all online redo log files in a group.
my undestandint of the sentence is following for example
group a includes file(a1, a2)
group b includes file(b1, b2)
LGWR write file sequence: write a1, a2 concurrently; afterwards write b1, b2 concurrently.
my question is following:
1、 my understanding is right?
2、 if my understanding is right, I think that separate log file in a group should save in different disk. if not, it cann't guarantee correctly recovery.
my opinion is right?
thanks everyone!

Hi,
>>That is multplexing...you should always have members of a log file in more than 1 disk
Exactly. You can keep multiple copies of the online redo log file to safeguard against damage to these files. When multiplexing online redo log files, LGWR concurrently writes the same redo log information to multiple identical online redo log files, thereby eliminating a single point of redo log failure. In addition, when multiplexing redo log files, it is preferable to keep the members of a group on different disks, so that one disk failure will not affect the continuing operation of the database. If LGWR can write to at least one member of the group, database operation proceeds as normal.
Cheers
Legatti

Redo log members in a group

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