Backup online redo log files
Hi All
Can you please explain for me the main reason that we do not have to backup the online redo log using RMAN ?
Thanks
The online redo logfiles are necessary to perform a complete recovery of the database. During database recovery, Oracle will apply the archived redo logfiles and online redo logfiles to roll the database forward and finally remove uncommitted transactions. If any of the online redo logfile group is active and missing, the database recovery will be incomplete and the database needs to be opened with restlogs, causing a new database incarnation.
You have to shutdown the datrabase to be able to perform a backup of the online redo logfiles, or find another method to create a time based snapshot of the data to prevent data movement while the redo logfiles are in use in order to keep datafile headers, controlfile and redo logfiles in sync. It is for that reason that you multiplex and mirror redo logfiles.
Similar Messages
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Status of online redo log file INVALID warning appears during online backup
Hi All,
I have a peculiar problem in one of the SAP ECC 6.0 systems. The daily online backup is getting completed with warnings.
Please find below the warnings in DB12 logs:
BR0335W Status of online redo log file /oracle/AS0/mirrlogB/log_g18m2.dbf is INVALID
BR0274W File '/oracle/AS0/mirrlogB/log_g18m2.dbf' not found
BR0335W Status of online redo log file /oracle/AS0/mirrlogA/log_g50_m2.dbf is INVALID
BR0274W File '/oracle/AS0/mirrlogA/log_g50_m2.dbf' not found
BR0335W Status of online redo log file /oracle/AS0/mirrlogB/log_g51_m2.dbf is INVALID
BR0274W File '/oracle/AS0/mirrlogB/log_g51_m2.dbf' not found
BR0335W Status of online redo log file /oracle/AS0/mirrlogA/log_g52_m2.dbf is INVALID
BR0274W File '/oracle/AS0/mirrlogA/log_g52_m2.dbf' not found
BR0335W Status of online redo log file /oracle/AS0/mirrlogA/log_g53_m2.dbf is INVALID
BR0274W File '/oracle/AS0/mirrlogA/log_g53_m2.dbf' not found
BR0335W Status of online redo log file /oracle/AS0/mirrlogA/log_g54_m2.dbf is INVALID
BR0274W File '/oracle/AS0/mirrlogA/log_g54_m2.dbf' not found
BR0335W Status of online redo log file /oracle/AS0/mirrlogA/log_g55_m2.dbf is INVALID
BR0274W File '/oracle/AS0/mirrlogA/log_g55_m2.dbf' not found
BR0335W Status of online redo log file /oracle/AS0/mirrlogA/log_g56_m2.dbf is INVALID
BR0274W File '/oracle/AS0/mirrlogA/log_g56_m2.dbf' not found
BR0335W Status of online redo log file /oracle/AS0/mirrlogB/log_g57_m2.dbf is INVALID
BR0274W File '/oracle/AS0/mirrlogB/log_g57_m2.dbf' not found
BR0335W Status of online redo log file /oracle/AS0/mirrlogA/log_g58_m2.dbf is INVALID
BR0274W File '/oracle/AS0/mirrlogA/log_g58_m2.dbf' not found
BR0335W Status of online redo log file /oracle/AS0/mirrlogB/log_g59_m2.dbf is INVALID
BR0274W File '/oracle/AS0/mirrlogB/log_g59_m2.dbf' not found
For the above mentioned alerts I followed the recommendations of SAP Note 491160. I dropped and recreated the mirrorlog files. But the next day again when I checked the backup it finished with warnings. At the database level there is no problem
SQL> select * from v$logfile;
GROUP# STATUS TYPE
MEMBER
IS_
59 ONLINE
/oracle/AS0/origlogB/log_g59_m1.dbf
NO
59 ONLINE
/oracle/AS0/mirrlogB/log_g59_m2.dbf
NO
GROUP# STATUS TYPE
MEMBER
IS_
58 ONLINE
/oracle/AS0/origlogA/log_g58_m1.dbf
NO
58 ONLINE
/oracle/AS0/mirrlogA/log_g58_m2.dbf
GROUP# STATUS TYPE
MEMBER
IS_
NO
57 ONLINE
/oracle/AS0/origlogB/log_g57_m1.dbf
NO
57 ONLINE
GROUP# STATUS TYPE
MEMBER
IS_
/oracle/AS0/mirrlogB/log_g57_m2.dbf
NO
56 ONLINE
/oracle/AS0/origlogA/log_g56_m1.dbf
NO
GROUP# STATUS TYPE
MEMBER
IS_
56 ONLINE
/oracle/AS0/mirrlogA/log_g56_m2.dbf
NO
55 ONLINE
/oracle/AS0/origlogA/log_g55_m1.dbf
NO
54 ONLINE
/oracle/AS0/origlogA/log_g54_m1.dbf
GROUP# STATUS TYPE
MEMBER
IS_
NO
54 ONLINE
/oracle/AS0/mirrlogA/log_g54_m2.dbf
NO
53 ONLINE
GROUP# STATUS TYPE
MEMBER
IS_
/oracle/AS0/origlogA/log_g53_m1.dbf
NO
53 ONLINE
/oracle/AS0/mirrlogA/log_g53_m2.dbf
NO
GROUP# STATUS TYPE
MEMBER
IS_
52 ONLINE
/oracle/AS0/origlogA/log_g52_m1.dbf
NO
52 ONLINE
/oracle/AS0/mirrlogA/log_g52_m2.dbf
NO
GROUP# STATUS TYPE
MEMBER
IS_
51 ONLINE
/oracle/AS0/origlogB/log_g51_m1.dbf
NO
51 ONLINE
/oracle/AS0/mirrlogB/log_g51_m2.dbf
GROUP# STATUS TYPE
MEMBER
IS_
NO
50 ONLINE
/oracle/AS0/origlogA/log_g50_m1.dbf
NO
50 ONLINE
GROUP# STATUS TYPE
MEMBER
IS_
/oracle/AS0/mirrlogA/log_g50_m2.dbf
NO
8 ONLINE
/oracle/AS0/origlogB/log_g18m1.dbf
As you can see from the above output at the database level everything is fine. So why during backup it is giving me warnings in DB12. Any help with this regard will be appreciated.
Regards
Mitesh NairHi Joe,
My OS is HP-UX. I dont think its a permission problem. Please find below the contents of origlogA and mirrlogA
predbci2:/oracle/AS0/origlogA#ls -rtl
total 1433712
drwxrwxrwx 2 oraas0 dba 96 Oct 15 03:27 cntrl
-rw-rw---- 1 oraas0 dba 104858624 Dec 4 01:50 log_g52_m1.dbf
-rw-rw---- 1 oraas0 dba 104858624 Dec 4 03:51 log_g50_m1.dbf
-rw-rw---- 1 oraas0 dba 104858624 Dec 4 05:51 log_g54_m1.dbf
-rw-rw---- 1 oraas0 dba 104858624 Dec 4 07:52 log_g53_m1.dbf
-rw-rw---- 1 oraas0 dba 104858624 Dec 4 09:50 log_g55_m1.dbf
-rw-rw---- 1 oraas0 dba 104858624 Dec 4 10:50 log_g56_m1.dbf
-rw-rw---- 1 oraas0 dba 104858624 Dec 4 12:41 log_g58_m1.dbf
predbci2:/oracle/AS0/mirrlogA#ls -rtl
total 1433728
-rw-rw---- 1 oraas0 dba 104858624 Dec 4 01:50 log_g52_m2.dbf
-rw-rw---- 1 oraas0 dba 104858624 Dec 4 03:51 log_g50_m2.dbf
-rw-rw---- 1 oraas0 dba 104858624 Dec 4 05:51 log_g54_m2.dbf
-rw-rw---- 1 oraas0 dba 104858624 Dec 4 07:52 log_g53_m2.dbf
-rw-rw---- 1 oraas0 dba 104858624 Dec 4 09:50 log_g55_m2.dbf
-rw-rw---- 1 oraas0 dba 104858624 Dec 4 10:50 log_g56_m2.dbf
-rw-rw---- 1 oraas0 dba 104858624 Dec 4 12:41 log_g58_m2.dbf
Regards
Mitesh -
What is online redo log files???
Dear All,
I m bit confused with redo log files.what is need of back up of redo log files?????As i m new in the Basis please tell me i always get confused with redo log files and archive files.
Thanx and reagard's
AshokIn Oracle you have a number of online redo log files.
In an typical SAP installation you have two directories:
origlogA and origlogB
origlogA contains online redo log 1 and 3 and
origlogB contains online redo log 2 and 4.
In most installation you also have mirrlogA and mirrlogB, which the name tells, is mirrors of origlogA and origlogB.
Now, the online redo logs are circular,
so when 1 gets full oracle jumps to number 2.
At the same time oracle's archiver process starts to copy
online redo log number 1 to a file on disk.
This files are also known as archive redo logs.
In an recovery situation you might do with just the online redo logs,
but usually a combination of both online and archive redo logs is needed.
During database backup, you also backup the online redo logs
You also need to backup (backup twice then delete) archive redo logs.
the archive redo logs are your way back from the restored database to the last transaction of the database.
If one archive redo log is missing, you have to stop you recovery there and loose the rest of the transactions done in the database. -
Non-multiplexed online redo log file damaged
how to fix if non-multiplexed online redo log file damaged , looking for info for both current & inactive..
If you only want to practice your skills these are good scenarios to do it. But if you are currently facing this problem then you are in big troubles if it happens to be the CURRENT. When this issue appears I suggest you not to shutdown the instance you should be aware that information written on the redo log is the backup of the running transactions in memory. If both get lost data is lost, if either one survives your chances to recover data are high.
~ Madrid
http://hrivera99.blogspot.com -
Moving the online redo log files to different location
We just installed few more drives into our sandbox system and I want to move the online redo log files for better performance. We've got the SAPARCH directory moved to a different location.
Does anyone know how/where I can change the parameters so redo log files are pointed at different drives? It's not in the <b>init<SID>.ora</b> file...
Regards,
SumitHi Sumit,
The following link contains information about moving the redo logs:
http://www.stanford.edu/dept/itss/docs/oracle/9i/server.920/a96521/onlineredo.htm
Best regards,
Alwin -
Physical Standby Online Redo log files,
Hi,
I'm trying to create a physical standby database (10.2.0.3). I'm a little confused about the requirement for online redo logs on the standby.
in my standby alert log I get the following when I issue:
SQL> alter database recover managed standby database disconnect from session
"ORA-00313: open failed for members of log group 1 of thread 1
ORA-00312: online log 1 thread 1: '/appl/oradata/prod/prod_1_redo_01_02.log'
ORA-27037: unable to obtain file status
SVR4 Error: 2: No such file or directory
Additional information: 3"
/appl/oradata/prod/prod_1_redo_01_02.log is the path to the location of the online redo logs on the production system. This file does not exist on the standby filesystem so the error is correct.
I assume that it gets this information from the standby control file I created on the production system and copied over to the standby.
Do I need to copy the online redo logs from the primary over to the standby site or do I need to create online redo logs on the standby?
Does the standby need to have redo log files?
I'm not talking about 'standby log files' of the type created using 'alter database add standby log file'. I've not got that far yet.
I just need to establish if a physical standby requires online redo log files?
Thanks in advance,
user234564I wanted to update this thread since I've been dealing with the exact same errors. The basic question is: "does a physical standby need the online redo logs?"
Answer: Not really, until one wants to switchover or failover (and become a primary database). Furthermore, whenever the MRP process is started, Oracle prepares for a possible switchover/failover by "clearing" the online redo logs (MetaLink note# 352879.1). It is not a big deal, since Oracle will build the actual redo files when the "alter database open resetlogs" is accomplished during a "role transition."
In our situation, we have decided to use our standby for nightly exports. We stop MRP, open the database read-only, then restart MRP. We built these standby DBs with RMAN. The RMAN duplicate process will not build the online redo log files until the database is opened for read/write (with resetlogs). However, we haven't had a need for read/write (i.e. a switchover).
Thus, every morning we have been getting the same errors that "user234564" posted above. At first the errors seemed scary, then we realized they were just a nusiance. In order to clean things up, all I did was just "cp" our stanby redo logs (SRL) into our online redo directories ensuring the names matched what was in v$logfile. When I restarted MRP, the alert log clearly showed Oracle clearing these "newly found" online redo logs. -
Commit Completes although current online redo log file have been removed.
Although i have removed current online redo log file in linux os (Oracle Linux),when i type "commit" it says that "commit complete".
Is this fair for this princip?*:" if Only when all redo records associated with a given transaction are safely on disk in the online logs is the user process notified that the transaction has been committed."*
I think that it can lead to loss of data in some cases..I'm using Oracle 11g R2 on OEL (x64)..
Can anyone explain me ? I'm getting stuck in this situation..
P.S : I haven't multiplexed current ORL group files...Javid wrote:
Although i have removed current online redo log file in linux os (Oracle Linux),when i type "commit" it says that "commit complete".
Is this fair for this princip?*:" if Only when all redo records associated with a given transaction are safely on disk in the online logs is the user process notified that the transaction has been committed."*
I think that it can lead to loss of data in some cases..I'm using Oracle 11g R2 on OEL (x64)..
Can anyone explain me ? I'm getting stuck in this situation..
In *nix, a file that is open by a process isn't really deleted until the process that has it completes. So even though you 'deleted' a redo log, oracle is still holding it. As soon as you stop your database (maybe even as soon as the db does a log switch) the redo will really be gone and no longer available. consider the implications for archive logging.
P.S : I haven't multiplexed current ORL group files...You need to fix that. the online logs are the achilles heel of the database. That's why it is standard practice to multiplex them. -
Hello,
How can I make a backup with redo log files using the following parameters?
backup_type = online_cons
backup_dev_type = disk_copy
-->archive_function = save_delete (It could be changed. Maybe it is the source of the error)
The copy is made, but an error occurs when it tries to copy the redo log files. The log shows the following message:
BR0291I BRARCHIVE will be started with options '-U -d disk_copy -c force -p initFDP_local.sap -cds'
BR0002I BRARCHIVE 6.40 (43)
BR0169I Value 'disk_copy' of parameter/option 'backup_dev_type/-d' ignored for 'brarchive' - 'disk'assumed
BR0181E Option '-cds' not supported for 'disk'
BR0007I End of offline redo log processing: adxexvpd.log 2008-02-06 03.41.57
Thanks in advance,
Ricard.
Edited by: Oscar Barrabes on Feb 6, 2008 10:08 AMHi Ricard,
You are right, you need to change the entry
archive_function = save_delete
to
archive_function = save
in init<SID>.sap
Nahum -
Accidently Deleted Online Redo Log Files
Dear friends
Just to give a try, I deleted online redo log files from the disk after clearn shutdown (In Test Environment Not A Production Database), then i started the dabase, I know we need atleast two online redo files for database to work properly. now my point of question is how can i create new online redo files ?
I have 2 redo logfile groups each with one member. In group 2 i have added new member for the deleted one using add logfile member ....... to group 2. but when i try todo the same to add logfile member to group1 I am not abale to do so. because its saying that this is the current logfile member. then I tried manual log switching to use next logfile member but database is not allowing as the database is just mounted not opened. plsease if any body helps me out to sort out this problem it will be a great help.
Anandkumar S.M
Oracle DBA
rC6Exv3hello ur instruction u have is some what bit rite. but i was not able to solve the problem
finally i solved the problem with these commands after database is mounted
recover database until cancel Enter
then I select the cancel option when it provide the user with the options
after cancelling the recover i issued the following command
alter database open resetlogs;
this method sorted out my problem
anyway very very thanks for ur root hints from where i got the Idea to recover online redo logfiles
Thank u very much -
Purpose of ONLINE REDO LOG FILES - Media or Instance recovery or BOTH ?
Hi
Currently studying this topic for the 1z0-031 exam and am a little confused.
my books (from instructor led class) say
-redo logs are a mean to provide redo transactions in the event of a DATABASE recovery
-redo log buffer gets flushed to redo log files to provide a recovery mechanism in case of MEDIA FAILURE
Then it says
-Online redo log files are used in a situation such as an INSTANCE FAILURE to recover uncommitted data which has not yet been written to the data files
- online redo log files are used for RECOVERY only.
Am i misunderstanding? Or are redo log files for both MEDIA and INSTANCE recovery? Or just INSTANCE ?
confused....
AmanjitOnline Redo Log Files are used in a sense for both Media and Instance Recovery. If your database is in NoArchive Mode then you will only be able to use the Redo Log Files for instance recover. But if you are running in Archive Log Mode then Redo Log Files are archived and will allow you to recover from media failure.
-
Optimal online redo log file size
hello to all,
I have installed just now 11gr2 patching 2.
I found
The Redo Logfile Size Advisor can be used to determine the least optimal online redo log file size based on the current FAST_START_MTTR_TARGET setting and MTTR statistics.
Which means that Redo Logfile Size Advisor is enabled only if FAST_START_MTTR_TARGET is set.
for now this installation is not a production instance (only for my testing) I am still on 10g
my question is:
is't important to set FAST_START_MTTR_TARGET, in 11g or that all old infos?, because from my query I see OPTIMAL_LOGFILE_SIZE isn't set.
SELECT TARGET_MTTR,ESTIMATED_MTTR,WRITES_MTTR,WRITES_LOGFILE_SIZE, OPTIMAL_LOGFILE_SIZE FROM V$INSTANCE_RECOVERY;TARGET_MTTR ESTIMATED_MTTR WRITES_MTTR WRITES_LOGFILE_SIZE OPTIMAL_LOGFILE_SIZE
0 20 0 0
and
SELECT a.group#, b.member, a.status, a.bytes
FROM v$log a, v$logfile b
WHERE a.group#=b.group#
GROUP# MEMBER STATUS BYTES
6 /u03/oradata/TEST/redo06.log CURRENT 1048576000
5 /u03/oradata/TEST/redo05.log INACTIVE 1048576000
4 /u03/oradata/TEST/redo04.log INACTIVE 1048576000
3 /u03/oradata/TEST/redo03.log INACTIVE 1048576000
2 /u03/oradata/TEST/redo02.log INACTIVE 1048576000
1 /u03/oradata/TEST/redo01.log INACTIVE 1048576000
thanks for any doc or info you will pointing mefor now this installation is not a production instance (only for my testing) I am still on 10g
my question is:
is't important to set FAST_START_MTTR_TARGET, in 11g or that all old infos?,There is no difference for FAST_START_MTTR_TARGET in 10g and 11g.
For 10g
http://download.oracle.com/docs/cd/B19306_01/server.102/b14237/initparams068.htm#i1127412
For 11g
http://download.oracle.com/docs/cd/B28359_01/server.111/b28320/initparams079.htm
Both documentation have exact text, means it will work exactly in 11g as 10g.
But do'nt see this like (because its not a official documentation link... as it is different from official doc's text though)
http://www.stanford.edu/dept/itss/docs/oracle/10g/server.101/b10755/initparams069.htm
Regards
Girish Sharma -
What is the difference between undo tablespace and online redo log files.
what is the difference between undo tablespace and online redo log files. I am confused
as per my knowledge undo tablespace is used to store the undo information when a table is being updated so that, just incase we need to rollback a transaction we know what was present in the table earlier.
when a transaction fails the SMON performs the rollback of the data.
This undo data is stored in the undo tablespace and read consistency if any is enforced.
is my understanding till here correct?
Now, can this undo data/before image not be stored in the redo log buffer and online redolog files?
can redo-log files not store this information?
in fact, is it that when undo tablespaces exist in a database, the undo data/before image is stored in both the undo tablespace and also the redo log files?
kindly clarify my doubt.
thank you.This question has been asked many times before. The answer is always the same.
Yes, redo contains the before image of data (and the after-image). Therefore, it **COULD** be used to roll back a transaction.
BUT... Redo is written sequentially. Using it to rollback your transaction would involve reading through all the redo written by maybe thousands of other people. It would be painfully slow.
Your transaction is, however, directly linked to just the UNDO that it generates (which is JUST the before image of the data). So, your undo is your undo and doesn't share space with anyone else's undo. Therefore, using it to roll back YOUR transaction is fast.
The fact that undo is only the before image of the data also makes it faster than wading through a sea of before and AFTER images as you'd find in redo. About twice as fast, in fact, since there's half the data. Roughly.
Redo also gets written and flushed to disk whenever there's a commit, 3 seconds are up or too much (1MB, actually) redo gets generated between flushes caused by other factors. Your redo gets flushed when those things happen, even if you haven't actually committed your transaction. And redo logs recycle themselves, meaning that your redo -even if your transaction hasn't been committed yet- can be over-written by later transactions. Try rolling back when that's happened, if redo was the source of your rollback data!
Undo, however, cannot be over-written if the transaction has not been committed. Ever. If you don't commit for three years, there will be three years' undo stored in your database (assuming you had the space, of course!).
I could go on, but that will do. Redo is there fore RECOVERY, after catastrophe. Undo is there for read-consistency (and the occasional change of mind). Two different functions. Two different mechanisms. Each one highly tuned to doing what it does, why it does it, most efficiently and effectively. -
Online redo log files being removed physically
Grid Infra version: 11.2.0.4
RDBMS Version: 11.2.0.4
Although this is a RAC DB, this is not a RAC-specific question. Hence posting it here.
Few months back, I remember issuing a command similair to below (DROP LOGFILE GROUP ...) and the redo log files were still physically present in the diskgroup.
If I remember correctly, the file is not deleted physical so that we can use the REUSE functionality (ALTER DATABASE ADD LOGFILE MEMBER '+REDO/orcl/onlinelog/redo1b.log' reuse to group 11; ) ie. you can use the REUSE command to add the logfile of the same name which is physically present in OS Filesystem/Diksgroup to redo log group.
But today, after I issued the below command, I checked the diskgroup location from ASMCMD
SQL> alter database drop logfile group 31;
Database altered.
From ASMCMD, I can that the file has disappeared physically. Is this a new feature with 11.2.0.4 or am I missing something here ?
ASMCMD> ls +DATA/msblprd/onlinelog/group_31.548.833154995
ASMCMD-8002: entry 'group_31.548.833154995' does not exist in directory '+DATA/msblprd/onlinelog/'Just to add to what Aman has said.
It is a bad practice not to let OMF decide the placement of Online redo logs because of this issue especially when you use ASM.
Executing rm command in Linux/Unix is easy but Dropping ASM aliases in the disk group can be a hassle.
This is documented.
"When a redo log member is dropped from the database, the operating system file is not deleted from disk. Rather, the control files of the associated database are updated to drop the member from the database structure. After dropping a redo log file, ensure that the drop completed successfully, and then use the appropriate operating system command to delete the dropped redo log file."
http://docs.oracle.com/cd/E11882_01/server.112/e25494/onlineredo.htm#ADMIN11324
BTW . You don't even need to set db_create_online_log_dest_n to enable OMF for ORLs.
SQL> show parameter log_dest
NAME TYPE VALUE
db_create_online_log_dest_1 string
db_create_online_log_dest_2 string
db_create_online_log_dest_3 string
db_create_online_log_dest_4 string
db_create_online_log_dest_5 string
SQL> show parameter db_create_file_dest
NAME TYPE VALUE
db_create_file_dest string +MBL_DATA
alter database add logfile thread 4
group 31 ('+MBL_DATA','+MBL_FRA') size 4096M,
group 32 ('+MBL_DATA','+MBL_FRA') size 4096M,
group 33 ('+MBL_DATA','+MBL_FRA') size 4096M,
group 34 ('+MBL_DATA','+MBL_FRA') size 4096M ;
Database altered.
And redo logs will be neatly placed as shown below
INST GROUP# MEMBER STATUS ARC
4 31 +MBL_DATA/bsblprd/onlinelog/group_31.276.832605441 UNUSED YES
+MBL_FRA/bsblprd/onlinelog/group_31.297.832605445 UNUSED YES
32 +MBL_DATA/bsblprd/onlinelog/group_32.547.832605451 UNUSED YES
+MBL_FRA/bsblprd/onlinelog/group_32.372.832605457 UNUSED YES
33 +MBL_DATA/bsblprd/onlinelog/group_33.548.832605463 UNUSED YES
+MBL_FRA/bsblprd/onlinelog/group_33.284.832605469 UNUSED YES
34 +MBL_DATA/bsblprd/onlinelog/group_34.549.832605475 UNUSED YES
+MBL_FRA/bsblprd/onlinelog/group_34.359.832605481 UNUSED YES -
Hi,
Can anyone tell me what's the real difference between a backup file and a redo log file/archived redo log file and the scenarios (examples) when each of them can be used (for example, "......") ? Both are used for database/instance recovery. I have read the concepts of there 2 terms, but I need some additional information about the difference.
Thanks!Roger25 wrote:
What i still don't understand is how redo mechanism works; I know, redo logs records changes made to the database and it's used to re-do informations in case of a system failure/crash, for example. Ok, let's say I have a huge update, but when the system crash has occured, the transaction is neither comitted, nor rolled back. Then, how this redo is useful? If a system crash occur, all those updates aren't rolled back automatically? So the database state is as before executing that huge update? So in this case, 'what to redo'?No, with the system's crash, the transaction never gets a chance to get committed (and even rolled back) because a commit is only supposed to happen if there is an explicit or implicit commit statement is issued. Now, for the redo , with the statement, a commit marker is entered at the end of the redo stream of that transaction denoting that it's finally over now and for the corresponding transaction, the status is cleared from the transaction table that's stored in the Undo segment in which the Undo information of that transaction is stored. If you have given a huge update, the redo would be very highly required as you should be knowing that it's not all the time that the dirty buffers that are written to the data files unlikely the redo log files which are written every 3 econds. This means, there is a very fair chance that many changes have yet not even propagated to the data files for which the change vectors are now already there in the redo log files. Now, for the sake of clarity, assume that this transaction was actually committed! So now, without those changes be applied to the data files how Oracle can actually show the committed reults when the database next time would be opened? For this purpose, the redo change vectors are required. And for the uncommitted transactions , the applcation of the redo change vectors would keep on updating the Checkpoint numbers of the data files and would eventually get them synched with the control file and redo log files, without which the database would never be opened.
HTH
Aman.... -
Online Redo log file/ Archive Files
hi guyz,
is there any tool available for to view contents of redo log file, or archive file (WHAT"S INSIDE????)
i hope i've explained what i want
regards
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