RE: Optimized redo log access
- From: Jeremiah Wilton <jcwilton93@xxxxxxxxxxx>
- To: "Mark W. Farnham" <mwf@xxxxxxxx>, xiangdongzou@xxxxxxxxx, 'agonenil' <agonenil@xxxxxxxxx>, 'ORACLE-L' <oracle-l@xxxxxxxxxxxxx>
- Date: Sun, 17 Aug 2014 13:11:51 -0700
Amihay pointed out that I probably meant group instead of member.
JW
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<div>-------- Original message --------</div><div>From: Jeremiah Wilton
<jcwilton93@xxxxxxxxxxx> </div><div>Date:08/17/2014 12:19 PM (GMT-08:00)
</div><div>To: "Mark W. Farnham" <mwf@xxxxxxxx>, xiangdongzou@xxxxxxxxx,
'agonenil' <agonenil@xxxxxxxxx>, 'ORACLE-L' <oracle-l@xxxxxxxxxxxxx>
</div><div>Subject: RE: Optimized redo log access </div><div>
</div>Back when it mattered which disk device we accessed for a specific
operation, this was pretty easy to achieve.
You just alternate disk(s) by member. For instance, if you have two dedicated
disks for online logs, member 1 would be on disk A and member 2 on disk B. That
way when we switch from member 1 to member 2, the archiver reads from disk 1
while we write to the online log on disk 2. You can see easily how we could
even do this and keep multiplexing with 4 disks.
I doubt that you get much benefit trying to do this kind of thing on modern
storage.
Jeremiah
Sent from my Verizon Wireless 4G LTE smartphone
-------- Original message --------
From: "Mark W. Farnham"
Date:08/17/2014 6:13 AM (GMT-08:00)
To: xiangdongzou@xxxxxxxxx, 'agonenil' , 'ORACLE-L'
Subject: RE: Optimized redo log access
I also do not know a way to make the archiver read a preferred member.
However, you may be able to get the read from a preferred physical disk
depending on your volume manager.
In ASM this would be by setting (or your preference being the default) the asm
preferred read failure group as shown in this example from the manual so that
your preferred read is the first one:
alter system set asm_preferred_read_failure_groups =
'DG2.DG2_0000','DG3.DG3_0000'
In some other volume managers there are possibilities for influencing or
controlling the preferred read of a volume constructed from plexes on different
physical media.
The starting point recommendation for multiple members is they should be on
media of similar capabilities and load, so the archiver (unless they slipped it
in when I wasn’t paying attention) does not directly have a toggle for
preference by member.)
Good luck. (Of course feeding arch is the reason some folks put redo on SSD,
while benchmarkers run around “debunking” the idea of redo on SSD because they
can show it does not speed up writes to compared to isolated physical HD
volumes when they compare to flash SSD [not battery backed DRAM SSD] with arch
turned off.) Removing arch reads from your diskfarm by relocating redo to SSD
will in fact “deheat” your disk farm and remove the competition for seeks for
writes and bandwidth for arch reads. Since redo is usually small relative to
the database disk farm, this may be cost effective, depending on your situation.
mwf
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On
Behalf Of xiangdongzou
Sent: Sunday, August 17, 2014 5:27 AM
To: agonenil; ORACLE-L
Subject: 回复: Optimized redo log access
archiver process can't read only special member.Oracle decicde which
member shoulde read.
2014-08-17
I AM AN ORACLE FANS!
Skype:Frank.oracle
Email:xiangdongzou@xxxxxxxxx
发件人：amihay gonen <agonenil@xxxxxxxxx>
发送时间：2014-08-17 16:51
主题：Optimized redo log access
收件人："ORACLE-L"<oracle-l@xxxxxxxxxxxxx>
抄送：
Hi , I've system that have multiplex redo log (2 members per group) and
multiplex destinations .
Due to performance consideration I would like to configuration the archiver
process to read only from one member (to reduce load on the specific device).
I'm not aware of such option to tell oracle which member to read .
Does anyone know if it is possible ?
Amihay .
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