My understanding is that most modern disks have track
buffers anyway which would obviate the need for
this...
(I'll happily stand corrected if anyone knows better)
hth
connor
- KC <kchan_at_speednet.com.au> wrote: > Connor,
>
> Thanks for your input. I agreed with you on what you
> said about the cache,
> however what I was asking is the read-ahead that the
> file system provided,
> for a physical read request, the file system
> actually read more blocks into
> the buffer, so the next physical read request can be
> satisfied from memory.
> I was wondering with direct I/O, is this still
> true?? Does VxFS read-ahead
> when it process a read request?? May be there is no
> such thing as read-ahead
> or it is irrelevant in this context, please correct
> me if my question
> doesn't make any sense!
>
> KC
>
>
> -----Original Message-----
> To: Multiple recipients of list ORACLE-L
> <ORACLE-L_at_fatcity.com>
> Date: Thursday, June 28, 2001 1:27 AM
>
>
> >The argument for direct io is that if you already
> have
> >a large cache (the oracle one), then its not much
> use
> >having a second copy of that cache (the unix one) -
> >that memory could possibly be better used elsewhere
> >(supporting more users, large sort sizes etc etc
> etc)
> >
> >So having direct io is giving more of the caching
> >responsibility to the oracle buffer cache.
> >
> >hth
> >connor
> >
> > --- KC <kchan_at_speednet.com.au> wrote: > Dear list,
> >>
> >> Our shop is running Solaris 2.6, Oracle database
> >> 8.0.6 and Veritas VxFS file system. At present,
> all
> >> database file access thru the file system buffer
> >> cache, we decided to use the direct I/O mount
> option
> >> with VxFS for performance reason. There is one
> issue
> >> I am not sure about and hope someone on the list
> can
> >> give me a pointer, access database file thu the
> file
> >> system buffer cache gives us "read ahead"
> advantage,
> >> with direct I/O I think what you read is what you
> >> get (no read ahead functionality), is this an
> >> issue?? If it is an issue, how do you deal with
> it??
> >> WIth file system buffer cache, I think the
> database
> >> block size should be the same as file system
> buffer
> >> size and file system block size is irrelevant to
> how
> >> much system read or write, is this still true
> under
> >> direct I/O, I am not sure what dictate how much
> data
> >> to read or write??
> >>
> >> KC
> >>
> >
> >=====
> >Connor McDonald
> >http://www.oracledba.co.uk (mirrored at
> >http://www.oradba.freeserve.co.uk)
> >
> >"Some days you're the pigeon, some days you're the
> statue"
> >
>
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> Author: KC
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>
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Connor McDonald
http://www.oracledba.co.uk (mirrored at
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"Some days you're the pigeon, some days you're the statue"
Do You Yahoo!?
Get your free @yahoo.co.uk address at
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Received on Wed Jun 27 2001 - 14:25:39 CDT
