Tuning : log buffer space in 11gr2

Question

Hi,
version : 11202 on hpux
awr Top 5 events shows :
Top 5 Timed Foreground Events :
Event Waits Time(s) Avg wait (ms) % DB time Wait Class
log buffer space 12,401 29,885 2410 55.83 Configuration
My log_buffer size is :
SQL> show parameter log_buffer
NAME                                 TYPE        VALUE
log_buffer                           integer     104857600And the sga values are :
SQL> show parameter sga
NAME                                 TYPE        VALUE
sga_max_size                         big integer 15G
sga_target                           big integer 15GI wanted to know if there are guide lines for tuning log_buffer space .
Can just double it from 100m to 200m ?
Thanks

Answer 1

Yoav wrote:
Top 5 Timed Foreground Events :
Event                    Waits    Time(s)       Avg wait (ms) % DB time    Wait Class
log buffer space      12,401  29,885            2410              55.83     Configuration My log_buffer size is :
SQL> show parameter log_buffer
NAME                                 TYPE        VALUE
log_buffer                           integer     104857600I wanted to know if there are guide lines for tuning log_buffer space .
Can just double it from 100m to 200m ?
You're the second person this week to come up with this issue.
The ONLY sensible guideline for the log buffer is to let it default until you have good reason to change it. Reasons for change (even to the point of modifying a hidden parameter) are really application dependent.
The last couple of times something like this has come up the issue has revolved around mixing very large uncommitted changes with large numbers of small transactions - resulting in many small transactions waiting for the log writer to complete a large write on behalf of the large transaction. Does this pattern describe your application environment ?
For reference - how many public and how many private redo strands do you have, and how many have been active. (See http://jonathanlewis.wordpress.com/2012/09/17/private-redo-2/ for a query that shows the difference).
Regards
Jonathan Lewis