Re: linux DBA's: O_Direct

Nuno,

   Thanks for the excellent links. It appears that I do indeed have my pagecache parameters out if order. Apparently my sysadmins trust me more than they should...

   As for allowing my pagecache to grow to 25% of RAM (on a server running nothing but Oracle), I'm not so sure... 15% of my 8GB sounds like a pretty generous allottment for caching executables and filesystem I/O. Of course, the "right" values will differ for everybody... That said, I'll give a careful read to the links you provided before revising my settings. :-)

Cheers,
-- Mark.

Nuno Souto wrote:

>Quoting MARK BRINSMEAD <mark.brinsmead_at_shaw.ca>:
>
>
>
>>[...]
>>
>>Adding the entry:
>> vm.pagecache 5 15 10
>>to /etc/sysctl.conf should (if I *now* recall correctly) set the minimum,
>>maximum, and "target" filesystem buffers to 5%, 15%, and 10% of RAM
>>respectively.
>>
>>[...]
>>
>>
>
>
>Hmmm, I'd have a quick look at:
>http://www.redhat.com/magazine/001nov04/features/vm/
>near the end of the page, just in case:
>
>those values for pagecache don't sound good.
>
>A better choice would be 5 15 25.
>Ie, never make the max smaller than what the borrow value is.
>
>In general terms:
>
>the first parameter is the size of cache (relative to memory size) below
>which the vm will start to reclaim pages exclusively from process cache.
>the second parameter is the size of cache (relative to memory size) below
>which the vm will start to reclaim pages from both file system cache and
>process cache.
>the third parameter is the size of cache (relative to memory size) that vm
>will use for both process page cache and file system cache.
>in general, cache (both process and file) is reduced as memory is needed
>for running processes, within the boundaries defined above.
>
>This also does a darn good job of explaining the mechanics of all that
>(and the whys of the process/file cache):
>http://surriel.com/lectures/ols2003/
>
>Enjoy.
>Nuno Souto
>from sunny Sydney
>--
>http://www.freelists.org/webpage/oracle-l
>
>
>
>
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