Re: RAC in NAS

  • From: Nuno Souto <dbvision@xxxxxxxxxxxx>
  • Date: Sat, 29 Jul 2006 23:29:48 +1000

Mark Brinsmead wrote,on my timestamp of 29/07/2006 11:55 AM:

But here's the half where you're wrong. (Or at least, not completely "right".) Those hypothetical
"other" applications can just as easily be resposibly for the *increases* in the slabinfo stats as
they are they would be for "non-zero" values. After all, those values had to increase from zero
*some* *time*, didn't they. ;-)

sure, but the chance of any of them touching the count when you start an Oracle instance is remote. Remember that I said to watch the counter WHEN you start Oracle.

The easiest way for me is to use the native "watch" linux program
on cat /proc/slabinfo: it's not that big anyway and kio
shows up around line 22 or so on mine:
watch -n 2 cat /proc/slabinfo
as root does the trick nicely.

Then you can see the cb counter (second column IIRC)
ticking over when Oracle starts.  Or not of course, if no
aio is present!

As reliable as it'll ever get, I reckon.  Short of digging
into kernel memory and pulling out the actual cbs and
their pointer links to each process.

Why on earth hasn't Oracle provided an easy and reliable method
of finding this out (other than through the indirect async io statistic)
is baffling.  I think the problem is in every *n*x port, btw.
Not just Linux.  In fact, Linux is probably the only one where it is
relatively easy to (non)confirm aio via the slabinfo trick:
I'm not aware of an equivalent in Unix, short of strace?  And that
is not even very reliable...

-- Cheers Nuno Souto in sunny Sydney, Australia dbvision@xxxxxxxxxxxx --

Other related posts: