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who reads the redo logs [message #131007]

Wed, 03 August 2005 18:03

mjschwenger
Messages: 137
Registered: July 2005
Location: US

Senior Member

I have a problem with my development - they insist that an Oracle installation has problems as in the redo log drives they see both writes and reads. Their statement is that there should be no reads from the redo log at all, only writes or something is broken. Well for the last couple of years I have always seen reads and write in the redo logs drives, but I could not answer their question why and who read the redo logs in the transaction process.
Very heavy OLTP - ora10g, aix5.2, good queries and indexes, statistics, very busy transactions concurent on 8 base tables. 18,000 inserts per minute + the almost same level of selects and updates. Usually between 24 to 72 processes.
Could somebody gives me an idea what does Oracle do and does it really read from the redo logs. If not - who reads them?
Thanks a lot in advance.
mj

[Updated on: Wed, 03 August 2005 18:05]

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Re: who reads the redo logs [message #131026 is a reply to message #131007]

Wed, 03 August 2005 23:50

girish.rohini
Messages: 744
Registered: April 2005
Location: Delhi (India)

Senior Member

HI

Yes, Oracle do read redo logs. For instance, if database is in archive log mode, redo log needs to be archived, & thus read does happen for redo logs.
Also, during instance recovery redo logs are read.

Regds
Girish

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Re: who reads the redo logs [message #131120 is a reply to message #131026]

Thu, 04 August 2005 08:35

Mahesh Rajendran
Messages: 10708
Registered: March 2002
Location: oracleDocoVille

Senior Member
Account Moderator

LGWR writes to redolog files.
ARchiver reads from redolog files and write to archived log file.
You having archived log enabled?

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Re: who reads the redo logs [message #131131 is a reply to message #131007]

Thu, 04 August 2005 09:51

mjschwenger
Messages: 137
Registered: July 2005
Location: US

Senior Member

I'm in no arch, guys...
SQL> select log_mode from v$database;

LOG_MODE
------------
NOARCHIVELOG
SQL> show parameter log_archive_start

NAME TYPE VALUE
------------------------------------ ----------- ------
log_archive_start boolean FALSE

What else could read?
How can I determine that this is exactly Oracle that reads - xould be another operating system process doing something on the same drives (although I will not be happy with that!)?
AIX 5.2
Thanks a lot,mj

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Re: who reads the redo logs [message #131138 is a reply to message #131131]

Thu, 04 August 2005 10:21

Mahesh Rajendran
Messages: 10708
Registered: March 2002
Location: oracleDocoVille

Senior Member
Account Moderator

or Logminer?

what is the specific issue here?
Do you have any statspack / tracefiles that shows waitevents related to heavy logfile read and thus any problem with this?

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Re: who reads the redo logs [message #131858 is a reply to message #131007]

Tue, 09 August 2005 15:50

nmacdannald
Messages: 460
Registered: July 2005
Location: Stockton, California - US...

Senior Member

I would suggest putting the database in archivelog mode when you get a chance, then take a full backup before letting users on. You are far more trusting of disks than I am, or perhaps you use RAID1 (I would still be concerned). Media recovery is not possible, I am told, without the database being in archivelog mode.

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