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RE: aio on sun ufs problem

From: <k.sriramkumar_at_iflexsolutions.com>
Date: Thu, 3 Jun 2004 10:16:47 +0530
Message-ID: <10898BE7CA96D611988B000802255AAF0689B6F0@fmgrt.rt.i-flex.com>


Hi Zhu,

        My understanding is that... Oracle Server process reads always have to be synchronous .Server Process will have to wait till the data is read and returned. They can proceed with the next operation ONLY after they get the data(Kind of a pipeline) . Asynchronous read would not be useful for these processes.

Best Regards

Sriram Kumar

-----Original Message-----
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of zhu chao Sent: Wednesday, May 05, 2004 10:49 AM
To: oracle-l_at_freelists.org
Subject: Re: aio on sun ufs problem

That is the point. The cost and benefit of using lwp based aio on filesystem, is it worthy or not.

    I saw note saying the cost of thread management and context switch is big, using LWP based AIO. Does any has measured the cost? (http://www.ixora.com.au/q+a/0011/14171201.htm)

    Another question, does aio only means asynch write(non-blocking write), is there concept like asynch read? I did a test doing a full table scan on a table which is a raw device. The os is doing pread os call, not kaio(aioread...).

    If only write benefit from asynch IO, then only dbwr/lgwr will benefit from KAIO. So when dbwr and lwgr can catch up clean the dirty buffer, whether to using aio does not matters.As server process only does read on datafile, and server process used most of system resource on a big system.(server process does write only during direct read/write and creating tablespace,as far as I know).

    Just some thought and questions about this topic.

Regards
Zhu Chao.
----- Original Message -----
>

> ---
> Aio on solaris is enabled by default if you use disk_asynch_io =3D true. =
> You
> will see a failed system call to kaio and then pread pwrite processes =
> spawn
> to simulate aio via light weight threaded processing.
> You can verify this in the same way using truss against dbwr. I'm not =
> sure
> what -t does, but if you just truss on dbwr process you will see the
> behavior. I personally feel that dbwr_io_slaves when weighed against =
> these
> facts are better suted at simulating aio than the light weight threaded
> processes.
> - David

>
>



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Received on Wed Jun 02 2004 - 23:39:52 CDT

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