RE: Average size of reads from online redo logs by ARCH process

Hi Bruce,
On Steve's site I didn't find anything about determining size of read by ARCH. I know how to determine avg. writes size by LGWR. Now I want to know what is size of ARCH IOs (reading) in order to figure out what striping we need to implement to reduce possible IO contention. Ideally, we need to put every redo log on a separate disk but it's an expensive solution, so I'm looking to possibility of stripe it. I think if both reads and writes are small, we can have stripe size to set so the one single IO affects most of the time one single physical disk. Another complication is that we are on EMC and I'm not sure yet if caching will play significant role in writes performance.

You and KGopal. are right - I could use 10046 to figure that out.

Thanks,
Alex

From: "McCartney, Bruce" <BMcCartney_at_talisman-energy.com> on 16-11-2004 09:59 MST To:
<agorbatchev_at_amadeus.net>
<oracle-l_at_freelists.org>

cc:

Subject:
RE: Average size of reads from online redo logs by ARCH process

Alex,
you could strace the arch process to get detailed numbers. The read size is dependent on the underlying file system setup (i.e. raw devices, veritas file system or unix/windows file system). There is not direct relationship to the buffer_size for read (or write). check out steve adams site for some detailed info on redo i/o http://www.ixora.com.au/notes/

just curious, why do you care about the *read* size? the average *write* size can be calculated from :

select value from v$sysstat where name='redo blocks written'; /
select value from v$sysstat where name='redo writes';

a log block size is os dependent as shown in http://www.ixora.com.au/notes/log_block_size.htm

-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org]On Behalf Of Alexandre Gorbatchev Sent: Tuesday, November 16, 2004 9:12 AM To: oracle-l_at_freelists.org
Subject: Average size of reads from online redo logs by ARCH process

Hi all,
How do I figure out what is the average (or constant?) size of disk reads from online logs by ARCH process?
Is there any relation to _log_archive_buffer_size? It is 2048 log blocks by default, as far as I know, so on my platform it's 2Mb.

Thanks in advance,
Alex

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