RE: Average size of reads from online redo logs by ARCH process
- From: Alexandre Gorbatchev <agorbatchev@xxxxxxxxxxx>
- To: BMcCartney@xxxxxxxxxxxxxxxxxxx
- Date: Tue, 16 Nov 2004 19:18:46 +0100
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@xxxxxxxxxxxxxxxxxxx> on 16-11-2004
09:59 MST
To:
<agorbatchev@xxxxxxxxxxx>
<oracle-l@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of Alexandre Gorbatchev
Sent: Tuesday, November 16, 2004 9:12 AM
To: oracle-l@xxxxxxxxxxxxx
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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