RE: Testing Direct I/O
- From: "Khemmanivanh, Somckit" <somckit.khemmanivanh@xxxxxxxxxxxxxxxx>
- To: <dbvision@xxxxxxxxxxxx>
- Date: Tue, 14 Feb 2006 08:25:33 -0800
Thanks Nuno!!
Can you clarify this somewhat?
>>>If in your HPUX environment you are using the extensions
to the Veritas file system, I strongly suggest that
you don't bother with dio and concentrate instead
on optimising that environment: much less pain,
much more gain.<<<
Thanks!
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Nuno Souto
Sent: Tuesday, February 14, 2006 12:46 AM
Cc: oracle-l@xxxxxxxxxxxxx
Subject: Re: Testing Direct I/O
oracle-l-bounce@xxxxxxxxxxxxx apparently said,on my timestamp of
14/02/2006
11:33 AM:
> To further clarify, the saved SQL statements I have are from business
> transactions -- they're all select statements, no DML...
and here I am for 30 years laboring under the
misunderstanding that SELECTs are DML statements...
As opposed to DDL: Data Definition Language!
:)
Seriously: isolate a series of statements that are
relevant to your environment and application,
get a test bed together and establish a baseline
with cooked io. Then switch on direct io and test,
tune, test, tune, etcetc. Stop when happy or
satisfied that it's good or bad for your app.
Measure overall number of IO requests per second
and overall MB/sec throughput. Simple, really.
One word of warning: when you turn on dio, you are
implicitly forfeiting a lot of little optimisations
the file system software might actually be doing
for you, contingent on what type of file system
and maker you were using before. And you are then
replacing those by the direct, simple IO requests
to/from disk into Oracle buffers. As such expect
some slight degradation of raw IO speed, paid for
by gaining some CPU back from having to do a lot less
buffer shuffling.
I do recall some option back in older versions that
would let you use direct mapping of Oracle buffers
to OS buffers. Ie, no buffer-to-buffer copy.
Dunno if still valid in 9i or 10g. That was usually
a better way to go if one wasn't sure of what could
be done at dio level to help the db sw or if one wasn't
authorised to mangle hardware and OS configs to
spread IO better.
If in your HPUX environment you are using the extensions
to the Veritas file system, I strongly suggest that
you don't bother with dio and concentrate instead
on optimising that environment: much less pain,
much more gain.
--
Cheers
Nuno Souto
in sunny Sydney, Australia
dbvision@xxxxxxxxxxxx
--
//www.freelists.org/webpage/oracle-l
--
//www.freelists.org/webpage/oracle-l
Other related posts:
