RE: RAC in NAS

From: Kevin Closson <kevinc_at_polyserve.com>
Date: Sat, 29 Jul 2006 11:49:15 -0700
Message-ID: <5D2570CAFC98974F9B6A759D1C74BAD0E5AC24@ex2.ms.polyserve.com>

it simulates skgfaio in threads...no matter, still a good lower-half test

	From: Frits Hoogland [mailto:frits.hoogland_at_gmail.com] 
	Sent: Saturday, July 29, 2006 9:40 AM
	To: kevinc_at_polyserve.com
	Cc: oracle-l_at_freelists.org
	Subject: Re: RAC in NAS
	
	
	exactly my point!
	
	I've seen oracle doing async IO with the 2.4 kernel doing other

system calls (the kludgy stuff you mentioned), and oracle doing async IO with the 2.6 kernel (io_submit system call).

Ever looked at orion in conjunction with linux? It doesn't seem to do async IO.

frits

On 7/29/06, Kevin Closson <kevinc_at_polyserve.com> wrote:

>> 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.

...but the calls are not the same. If you strace 10g DBWR, after linking

		in
		libaio and setting filesystemio_options=direcIO, you
will see
		io_submit(2)
		calls which are new to 2.6 kernel. There really was no
"real" async IO
		prior to the 2.6 kerenl. There was some kludgy stuff
piggy-packed on 
		the socket interface of all things, but it was crazy.
		
		Then , of course, if $ORACLE_HOME/lib/libodm* is a real
ODM library you
		get
		async IO regardless of what libaio is and regardless of
what init.ora
		parameters you set...when ODM is linked in, all the
"async*" init.ora
		params
		are no-ops and filesystemio_options doesn't do anything
either. You just
		get
		async IO
		
		--
		http://www.freelists.org/webpage/oracle-l

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

Received on Sat Jul 29 2006 - 13:49:15 CDT