Syed
>>We are oftenly getting 'log file sync' and 'log file parallel wait'
wait event.
How much time is spent on these waits by the foreground processes ? Can
you post top 5 wait event section from statspack report or AWR report ?
Are you trying to tune a specific process or instance wide tuning ?
>>I feel, 16M is very big value for log_buffer.
That is not an universally true statement to make. You can have 100M log
buffer and still have stellar performance. Log buffer size must be
determined in conjunction with redo generation rate and commit rate.
>>redo_buffer can't be resized, as it depends on no. of datafiles.
Would you please post the document ID so that we can review this, please
? This doesn't sound correct. I don't know why log_buffer size would be
dependent upon # of datafiles.
>>The _log_io_size is 0. Can we play with this hidden parameter to bring
>> back the redo_buffer size to 3M?
LGWR flushes the log buffer when there is more than 1M to write or 1/3rd
full. So, any value for _log_io_size above 1M is meaningless. But, if
you set it too low, then LGWR might be overactive introducing latch
contention issues. Unless commit rate is excessive in your application
or an I/O problem with LGWR, there is no need to tweak these parameters.
In essence, does statspack report/AWR report /sqltrace shows that these
waits are excessive and must be tuned ?
Thanks Riyaj
Hello List,
We have recently upgrade our 9i Rel.2 database to 10g Rel.2, on AIX 5L OS.
We are oftenly getting 'log file sync' and 'log file parallel wait' wait event.
In 9i, we have solved this by enabling CIO to the filesystem.
Surprisingly, the log_buffer size is set to 16M, by default.
We tried to set multiple value, but, by default it takes 16M.
I feel, 16M is very big value for log_buffer.
When I go and search in the metalink, it says, its a bug and
redo_buffer can't be resized, as it depends on no. of datafiles.
Our server has 16cpus and 160 datafiles.
The _log_io_size is 0. Can we play with this hidden parameter to bring
back the redo_buffer size to 3M?
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