Re: db_file_multiblock_read_count and 10g

From: Greg Rahn <greg_at_structureddata.org>
Date: Sun, 25 Jan 2009 16:38:01 -0800
Message-ID: <a9c093440901251638x4832b28al31705251fd587295_at_mail.gmail.com>



On Sun, Jan 25, 2009 at 3:42 PM, <ukja.dion_at_gmail.com> wrote:
>>
>> IIRC _db_file_exec_read_count=8 and
>> _db_file_optimizer_read_count=((max I/O size)/DB_BLOCK_SIZE)), so
>> usually 1MB I/O size.
>
> I think you mean _db_file_optimizer_read_count=8 and
> _db_file_exec_read_count = ((max I/O size)/DB_BLOCK_SIZE)).

I did. Caught a bit of dyslexia for a moment.

> This is a reasonable assumption, but I'm not sure how Oracle determines the
> maximum I/O size. On my laptop, Oracle 10.2.0.1 and 11.1.0.6 show quite
> different _db_file_exec_read_count.
>
> In 10.2.0.1 : _db_file_exec_read_count = 5
> In 11.1.0.6 : _db_file_exec_read_count = 128
>
> It seems quite dependent on Oracle version, not just on OS and/or storage
> settings.

Going from memory and not looking at the code, I think the db cache size and number of processes also influence it, and I don't recall if this changed between releases or not.

I'll research this a bit more next week if I have free time.

-- 
Regards,
Greg Rahn
http://structureddata.org
--
http://www.freelists.org/webpage/oracle-l
Received on Sun Jan 25 2009 - 18:38:01 CST

Original text of this message