Re: direct I/O with VxFS

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
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-- 
Author: KC
  INET: kchan_at_speednet.com.au

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