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Re: RAC in NAS

From: Frits Hoogland <frits.hoogland_at_gmail.com>
Date: Sat, 29 Jul 2006 17:08:53 +0200
Message-ID: <fbb8fbcd0607290808i23eabef5g6e7f016dc8a019e9@mail.gmail.com>


funny. last time I checked it on an instance (also oracle 9, on RHAS2.1), I've set filesystemio_options and the system calls were different. having said that, I've straced orion on linux, and concluded orion is running synchronous on linux. (results are on my blog)

on the other hand, if the system call is the same, what kind of magic is involved which makes oracle do asynchronous IO? The system call must tell the operating system what kind of IO it wants to do, either by doing a call which implies the kind of synchronousity, or by setting a flag which alters the synchronousity.

frits

On 7/29/06, Nuno Souto <dbvision_at_iinet.net.au> wrote:
>
> Frits Hoogland wrote,on my timestamp of 29/07/2006 10:27 PM:
>
> > doesn't do a strace on the dbwr and lgwr do what you want to know?
> > it is simple, and it tells you all you want!
> > the calls of synchronous and asynchronous IO are different!
>
>
> not really. At least not in Linux RH3 and O9i: the calls show up
> as the same no matter if aio is being used or not. And the
> open flags show up the same as well. I'm assuming aio on file
> systems - aio on raw might be a different kettle, I have not tried
> strace there. In fact I have not tried raw with Linux, period.
> And I believe with 2.6 kernel raw becomes "deprecated", so things
> are getting harder on that front!
>
> The only way I've found to confirm that *something* is using aio kernel
> code is have a gander at slabinfo and then use stats in Oracle instance
> to see if the aio counters are ticking over.
>
> Direct IO however will show up nicely as an open flag with
> strace, no matter raw or cooked io!
>
>
> --
> Cheers
> Nuno Souto
> in sunny Sydney, Australia
> dbvision_at_iinet.net.au
> --
> http://www.freelists.org/webpage/oracle-l
>
>
>

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Received on Sat Jul 29 2006 - 10:08:53 CDT

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