Introduction
Redo Log Files(.log): Oracle maintains logs of all the transaction against the database,These transactions are recoreded in files called online redo log files(Redo logs) The main purpose of the redo log files is to hold information as recovery in the event of system failure,redo log stores a log of all changes made to the database the redolog files must perform well and be protected against hardware failures (through software or hardware fault tolerance).if redolog information is lost,one cannot recover the system when a transcation occurs in the database,it is entered in the redo log buffers,while the data blocks affected by the transactions are not immediately written to disk,in an oracle database there are at atleast three or more redolog files,oracle writes to redolog files in a cyclical order i.e after the first log file is filled ,it writes to the second log file,untill that one is filled .when all the redo log files have been filled,it returns to the first log file and begin overwrite its content with new transaction data.note if the database is running in ARCHIVELOG mode,the database will make a copy of the online redolog files before overwriting them
How to increase the size of the redo log files?
Steps :
` Add new groups with larger size
drop existing inactive members.
sql>select member from v$logfile;
eg: expected : 100m Current : 50M (recommended 1G-2G in live for faster performance)
Adding New Groups:
sql>ALTER DATABASE
ADD LOGFILE GROUP 4 '/oradata/prod/redo4.log' size 200m;
ALTER DATABASE
ADD LOGFILE GROUP 5 '/oradata/prod/redo5.log' size 200m;
ALTER DATABASE
ADD LOGFILE GROUP 6 '/oradata/prod/redo6.log' size 200m;
sql>select group#,members,bytes/1024/1024,status from v$log;
Use manual log switch to make use of new redo groups.
sql>alter system switch logfile;
Now drop inactive groups of different in size.
sql>ALTER DATABASE DROP LOGFILE GROUP 1;
sql>ALTER DATABASE DROP LOGFILE GROUP 2;
sql>ALTER DATABASE DROP LOGFILE GROUP 3;
IF found active - use log switch to make it inactive
sql>alter system switch logfile;
sql>select group#,members,bytes/1024/1024,status from v$log;
Managing Archive log files
logbuffer(1/3rdor3 secs)-lgwr-logfiles->archiver->arc log files
The process of turning online redo logfiles into offline
redolog files is known has archiving.
The offline redo logfiles are called Archivelog files.
with .arc ext
Its mandatory in production to enable archiving and optional in Development.
The content of archives can be used for recovery of datafiles.
Enabling Archive log mode:
Physical Dest - /archives/prod - .arc
mkdir -p /archives/prod
sql>archive log list
sql>show parameter log_archive_dest_1
format
sql>show parameter log_archive_format
sql>alter system set log_archive_dest_1='LOCATION=/archives/prod' scope=both;
sql>alter system set log_archive_format='%t_%r_%s.arc' scope=spfile;
%t - thread number associated with instance number1
%r - redo sequence
%s - log sequence number
sql>shutdown immediate
sql>startup mount
sql>alter database archivelog;
sql>alter database open;
sql>archive log list
sql>alter system switch logfile;
sql>exit
cd /archives/prod
redologfiles->arch(bg process) -> archivelogfile(.arc)
Here archiver is the background process writes from online
redo log files to off archivelog files when log switch occurs.
sql>show parameter log_archive_max_processes
We can have up to 30 max processes of archiver
$ps -ef | grep arc
default - 4
Note: Info on redolog it may be differ from your environment production,testing,dev naming conventions,and directory structure etc
THANKS FOR VIEWING MY BLOG FOR MORE UPDATES FOLLOW ME OR SUBSCRIBE ME
