Can we change log_buffer parameter online e.g. when all users are working..

Question

Hi,
Can we change log_buffer parameter online e.g. when all users are working.. ???
What is relation between redo buffer in sga and log_buffer parameter ?
SQL> show sga
Total System Global Area 3758096384 bytes
Fixed Size 1983152 bytes
Variable Size 553655632 bytes
Database Buffers 3187671040 bytes
Redo Buffers 14786560 bytes
SQL>
SQL> show parameter log_buffer
NAME TYPE VALUE
log_buffer integer 14338048
SQL>
SQL>
If the log_buffer parameter is 14 MB then why redo buffer is no as same size e.g.
14 MB
SSM

Answer 1

I am hoping your Oracle Consultant know what he's talking about.
According to Oracle Performance Guide,
http://download-west.oracle.com/docs/cd/B19306_01/server.102/b14211/memory.htm#sthref654
"On most systems, sizing the log buffer larger than 1M does not provide any performance benefit. Increasing the log buffer size does not have any negative implications on performance or recoverability. It merely uses extra memory.
The best method to determine if bigger redo buffer is needed is
SELECT NAME, VALUE
FROM V$SYSSTAT
WHERE NAME = 'redo buffer allocation retries';
The value of redo buffer allocation retries should be near zero over an interval. If this value increments consistently, then processes have had to wait for space in the redo log buffer. The wait can be caused by the log buffer being too small or by checkpointing. Increase the size of the redo log buffer, if necessary, by changing the value of the initialization parameter LOG_BUFFER. The value of this parameter is expressed in bytes. Alternatively, improve the checkpointing or archiving process.
Other than that, hight log file sync event indicate you need faster disk for your redo logfiles. However, please also post your commits per second and redo per second from your AWR report.
100M redo logs might be small for your environment.