I am trying to learn more about I/O under AIX. And one of things that is mentioned on few places is this filesystem cache hit ratio/rate. I understand what it is, but am not able to find out where can I get this number.
Closest what I got is 'sar -r $m $n' command and column idio/s, from manual:
"Reports the number of non paging disk I/Os per second."
This seems to be a quite usefull number, though I would need some other number to calculate hit/miss filesystem ratio.
I presume that the smaller file system cache the lower hit radio. So does anybody use this hit/miss cache ratio to tune/evaluate performance a server? Or perhaps to estimate proper amount of RAM for given server?
Another aspect in our situation is that we have mostly oracle DB running on servers and I read that they have own caching and filesystem cache is not important for them. Therefore can I ignore this hit cache ratio altogether?
Another question, if have AIX with oracle DB and some 100 GB of RAM, where numperm oscilates between 45 -65. Can it be interpreted that we can reduce RAM by some 20-40 GB without any performance hit?
That all :), I know topic is quite wide, but I would appreciate any advices or experiences
Pinned topic fs cache size, hit ratio and oracle DB
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Updated on 2012-10-08T11:44:50Z at 2012-10-08T11:44:50Z by SystemAdmin
SystemAdmin 110000D4XK6902 Posts
Re: fs cache size, hit ratio and oracle DB2012-10-08T11:44:50ZThis is the accepted answer. This is the accepted answer.Hi,
I have the same questions about cache utilization and Oracle.
Did you find something ? Or is there somebody who have answers about this ?
Thanks a lot