Re: Calculating Physical memory for Oracle Sessions

On 11/30/06, Jesse, Rich <Rich.Jesse_at_qg.com> wrote:
>
> Jared, wouldn't your formula multiply shared memory (e.g. Oracle SGA size
> as reported by "ipcs -ma") by the number of Oracle processes (except for
> procs that don't connect to the instance, like the listener)? I think using
> ps output that way would be like saying that adding 25% of "X" and 25% of
> "Y" must equal 50% of "X+Y".
>
> While I've never taken the time (had the time?) to dealve into it, I think
> that pmap is accurate iff shared memory is accounted for. The trick is to
> determine if any other process is accessing that shared memory.
>

Which is another way of saying that pmap is not accurate. ;)

My knee jerk is that this could be accomplished by making a "master" list of
> shared memory (possibly using pmap outputs) to evaluate against whatever
> subset of processes you would want to see.
>

I do it with ipcs and /proc/*/maps

This blog item mentions this problem, but doesn't really offer a solution:
>
>
> http://virtualthreads.blogspot.com/2006/02/understanding-memory-usage-on-linux.html
>

I've probably already read that blog.

Kinda wierd that no one's thought of a solution (even if it's only a 99%
> one) to this, ain't it?
>

I have a solution (for linux) that comes fairly close.

It involves a perl script to get a list of process ID's from ps, then calculates the memory usage from raw data in /proc/*/maps. There is also a small C program to get pagesize.

-- 
Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist

--
http://www.freelists.org/webpage/oracle-l