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  • Latest Post - ‏2012-10-08T11:44:50Z by SystemAdmin
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Pinned topic fs cache size, hit ratio and oracle DB

‏2012-04-20T08:41:43Z |

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
Updated on 2012-10-08T11:44:50Z at 2012-10-08T11:44:50Z by SystemAdmin
  • SystemAdmin
    6902 Posts

    Re: fs cache size, hit ratio and oracle DB


    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