How to Modifying the Size of Redo Logs ?

We must drop and re-create the redo to re-size the redo logs and that can be done online without interrupting database service.

Step - 1 Make sure the logfile you want to change is not the current or active log file.
Step - 2 Drop the logfile group you want to change.
Step - 3 Re-create the logfile group, re-sizing it as required.

SQL> select group#, status from v$log;

---------- ----------------
         1 INACTIVE
         2 INACTIVE
         3 CURRENT

Here we have to change log group 3 but it seems current so we have to make it inactive by switching logfile.

A CURRENT status indicates that the resulting dirty block that are associated with the redo in the logfile have not yet been check pointed which is required before we drop the logfile.

SQL> Alter system switch logfile;

SQL> Alter system switch logfile;

Checkpoint the system. This will remove the log file we want to drop from a possible active status.

SQL> Alter system checkpoint;

Now check the status of logfile again the status of group 3 is 'INACTIVE' now

SQL> select group#, status from v$log;

---------- ----------------
         1 CURRENT
         2 INACTIVE
         3 INACTIVE

Once the checkpoint is complete, we drop the online redo log group, and re-create it defining a new size for the redo log files.

SQL> Alter database drop logfile group 3;

Now add the logfile group with the new sizing information.

SQL> alter database add logfile group 3
   '\ORADATA\REDO\redo03b.log') size 500m REUSE;

Script of Memory Advice Report for 11g

col buffer_cache format a16 heading "Buffer Cache|Change"
col pga format a12 heading "PGA |Change"
col current_cache_mb format 99,999 heading "Current|Cache MB"
col target_cache_mb format 99,999 heading "Target|Cache MB"
col current_pga_mb format 99,999 heading "Current|PGA MB"
col target_pga_mb format 99,999 heading "Target|PGA MB"
col pga_secs_delta format 99,999,999 heading "Pga Time|Delta (s)"
col cache_secs_delta format 99,999,999 heading "Cache Time|Delta (s)"
col total_secs_delta format 99,999,999 heading "Total Time|Delta (s)"

set pagesize 1000
set lines 80
set echo on 
WITH db_cache_times AS 
    (SELECT current_size current_cache_mb, 
            size_for_estimate target_cache_mb,
            (estd_physical_read_time - current_time) 
       FROM v$db_cache_advice,
            (SELECT size_for_estimate current_size,
                    estd_physical_read_time current_time
               FROM v$db_cache_advice
              WHERE  size_factor = 1
                AND name = 'DEFAULT' AND block_size = 8192)
       WHERE name = 'DEFAULT' AND block_size = 8192),
 pga_times AS 
     (SELECT current_size / 1048576 current_pga_mb,
             pga_target_for_estimate / 1048576 target_pga_mb,
             estd_time-base_time pga_secs_delta 
        FROM v$pga_target_advice , 
             (SELECT pga_target_for_estimate current_size,
                     estd_time base_time
                FROM v$pga_target_advice 
               WHERE pga_target_factor = 1))
SELECT current_cache_mb||'MB->'||target_cache_mb||'MB' Buffer_cache,
       current_pga_mb||'->'||target_pga_mb||'MB' PGA,
       (pga_secs_delta+cache_secs_delta) total_secs_delta
  FROM db_cache_times d,pga_times p
 WHERE (target_pga_mb+target_cache_mb)
   AND (pga_secs_delta+cache_secs_delta) <0
 ORDER BY (pga_secs_delta+cache_secs_delta);

Multicasting in Linux

Check whether multicast is enabled or not.

Command : #ifconfig eth0

You cans see multicast is enabled in above output.

Disable Multicast

Command : #ifconfig eth0 -multicast

Enable multicast

Command : #ifconfig eth0 multicast