Thank you Mark and Brandon,
This is the kind of information I'm looking for; I've read Steve's stuff but
it's been a while and the AIX paper is new to me. I *think* we need to make
some changes in our approach, but right now, I just want to gather and study
as much information on the different options and approaches as possible.
So, if anyone has additional links, documents or experiences, I'd appreciate
the input.
thank you ... Robyn
On 7/9/07, Allen, Brandon < Brandon.Allen@xxxxxxxxxxx> wrote:
I'd be curious to hear anyone's reasons for preferring OS cache to DB
cache.
It seems pretty clear cut to me that it is better to allow Oracle to
manage its own cache since it has much more knowledge available internally
to help predict which blocks are most likely to be needed again. I've had
good results with CIO (Concurrent, a.k.a non-buffered, non-inode-locking
I/O) on AIX, but I did increase db_cache_size to make up for the lack of
filesystem buffering - in one case from 600M to 1500M, in another I just
used CIO from the beginning so there was no before/after comparison, but
performance has been excellent with CIO. In the case where I switched from
regular, buffered I/O to CIO and increased db_cache_size from 600M to 1500M,
the performance of a fixed set of batch jobs improved from an average
runtime of 166 minutes to 129 minutes - so a 22% reduction in runtime, but
it's difficult to say how much of that improvement was from switching to CIO
and how much was just due to the increase in db_cache_size alone.
Here's a great paper specifically on AIX CIO for more info:
http://www-03.ibm.com/servers/aix/whitepapers/db_perf_aix.pdf
