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Re: Oracle on Windows Vs. Linux

From: Nuno Souto <>
Date: Sat, 20 May 2006 21:39:50 +1000
Message-ID: <>

Kevin Closson wrote,on my timestamp of 20/05/2006 3:28 PM:

> The post you are responding to had to do with Jared's
> point about atime updates. Async or not, direct I/O
> is what circumvents mtime/atime updates.

didn't say it wasn't, Kevin. But it's not the be-all, end-all of efficient IO in Linux. And dio does circumvent mtime/atime updates but it's not what does it exclusively: if one selects noatime, one doesn't get dio.

What I am alerting to is that it's not only just turning these options on or off: the patch levels have to be checked as well and Metalink has to be scoured for any bugs. It's the case with 10gr1 and it certainly and most absolutely was the case with 9i and below:

I do recall the umpteen times folks reported here and elsewhere no change or incoherent results in their cooked/dio/aio testing and the problem was, in almost all cases, OS and/or Oracle incorrectly or incompletely patched!

And where it was incompletely patched, it was in most cases due to the sheer lack of information on this subject from both Oracle and Linux support, at the time of 9i and before. Even today it STILL is not easy to find: one has to dig long and hard for the correct combination of search words in Metaclick to get the juicy bits. It shouldn't be like that, but it is.

Yes, I know: Oracle claims that 10gr2 "has no bugs". But then again they claimed the same for 10g, 9ir2, etc, ad nauseum and we all know the stacks of "unpublished" bugs that await those who try to push the envelope in those versions. Wait for 11 and the stack of bugs on 10gr2 that will suddenly show up in Metalink as "only fixed in 11, upgrade or else...".

So: caveat emptor and test,test,test - and search Metalink. Of course - not you: those listening in.

> BTW, neither direct, nor async make I/O "faster". The DMA transfer
> takes as long as the I/O subsystem will facilitate. However,
> direct and/or async usually handles the same amount of I/O
> with improved processor efficiency...and that, generally improves
> overall system throughput.

Exactly. The various types of IO do little in terms of the disk or transfer speeds, if anything, as you well say.

But I'd still carefully check native disks with hdparm: some Linux ports do stupid things to obvious options in modern disks. Our test servers areu standard blades with native controllers/disks and particularly with SATA hardware things can go awfully "clunk"...

 > Oracle Disk Manager is about the
> most efficient I/O library for Oracle...should be, Oracle
> defined the library...but I digress.

It might be what Oracle thinks of IO, not what the OS thinks of IO. Namely and as an example: there is a world of difference on how Linux 2.4 and 2.6 perform disk IO at the low level SIO/queueing, OS interrupt handling level and its impact on the scheduler. All 3rd party IO libraries use that code no matter what else they might do. All potentially do benefit from running in 2.6 as opposed to 2.4, even if it's the highly patched - and efficient - RHEL3-Upd6.

Still early days in 2.6 but there might be one or two file systems getting into that game as well. My bet is on ReiserFS and XFS. I think IBM has completely dropped the ball with JFS on Linux. One of the latest Linux Journal editions has some interesting reading on all the above.

> I'm flashing back now..uh, right, it was 6.0.27 on Sequent
> DYNIX/ptx where we implemented direct+async I/O on filesystem
> files for the first time... ah, the good old days

Great work and badly needed at the time. But Linux is far behind modern Unix in many areas, as Mladen correctly pointed out a while ago. It's quite interesting to watch the evolution, deja vu.

Like Linus himself said not too long ago: "most of the OS theoretical research was done in the 70s and 80s, there has been nothing fundamentally new since then".

Nuno Souto
in rainy Sydney, Australia
Received on Sat May 20 2006 - 06:39:50 CDT

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