Re: linux /proc/sys/vm/pagecache for oracle

On Thu, 06 Apr 2006 09:27:37 +0200, Fabrizio Magni <fabrizio.magni_at_mycontinent.com> wrote:

>NetComrade wrote:
>>> In general, on any 2.6 kernel (not only redhat), you should use
>>> /proc/sys/vm/swappiness.
>>>
>>
>>
>> This looks to be a parameter affecting swapping processes, not file
>> system caching.
>>
>> Anyway, my 'cached' file systems seem to be not the ones oracle is
>> sitting on, as when I remounted in 'direct' cache didn't go away. The
>> fie system is vxfs and we are using ODM, so nothing should be cached..
>> which is why I was confused that cache is so big.
>
>Swappiness indicates how aggressive pages in memory are swapped out,
>even for fs cached pages, which is probably what you wish to avoid.
>
>It automates what the second parameter of pagecache was meant to do.
>
>As far as I remember /proc/sys/vm/pagecache was a 2.2 kernel features
>and redhat ported it on kernel 2.4 with AS 2.1.
>It has been dropped a long time ago.

I tried lowering swappiness from 60 to 10 and it didn't seem to affect the file cache.

From RedHat
(http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/ref-guide/s1-proc-directories.html): "swappiness — Determines how much a machine should swap. The higher the value, the more swapping occurs. The default value, as a percentage, is set to 60."

To me swapping means swapping processes out of memory, including their data structures. File System cache doesn't have anything to do with that, imho.

>Never used ODM on linux so I cannot help you there. Sorry.

ODM is something like "performance of raw devices with file system manageability"
.......
We run Oracle 9.2.0.6 on RH4 AMD
remove NSPAM to email Received on Thu Apr 06 2006 - 10:57:42 CDT